Diego Fernández de Medrano y Zenizeros

In this Basque name, the first surname is Medrano and the second is Zenizeros.

The Most Illustrious Reverend Diego Fernández de Medrano Zenizeros Lord of Sojuela, Valdeosera, and Entrena
Coat of arms of the Fernández de Medrano family on top of the coat of arms of Valdeosera
Born	Sojuela, La Rioja, Spain
Alma mater	University of Salamanca (Alumni)
Occupation(s)	Cleric, Nobleman, Author
Known for	Political treatises, service to the Spanish Crown
Notable work	Heroic and Flying Fame of the Most Excellent Lord Don Luis Méndez de Haro; Mirror of Princes
Title	Lord of Sojuela, Valdeosera, La Vega, and Entrena
Father	Diego Fernández de Medrano Zenizeros (Knight of Santiago, Lord of Sojuela)
Relatives	Tomás Fernández de Medrano (great-uncle), Diego de Medrano (great-uncle), Francisco Fernández de Medrano (grandfather), Diego Fernández de Medrano y Zapata (relative)

Diego Fernández de Medrano Zenizeros (in full, Spanish: Don Diego Fernández de Medrano Zenizeros, señor de la Villa de Sojuela, del Solar y Divisa de Valdeosera, de la Torre y de la Casa de la Vega en Rioja, etc.) was a 17th-century Spanish cleric, nobleman, and author, recognized for his political treatise, panegyric writings and his service to the Spanish Crown. A presbyter and lord of multiple noble estates—including the divisa and solar de Valdeosera and town of Sojuela, de la Torre and House de La Vega in La Rioja, and the Palace of Entrena—he held a prominent place within the religious, and intellectual landscape of his time. He served as a chaplain for both Luis Méndez de Haro, 2nd Duke of Olivares, and Pedro Coloma, Secretary of State for the Spanish Crown. He served two terms as the Chief Magistrate and Mayor of Valdeosera in San Román de Cameros, La Rioja. He is best known for authoring a political treatise in the mirror for princes genre, dedicated to Philip Prospero, Prince of Asturias, as well as a politics-based treatise-panegyric hybrid in honor of Luis Méndez de Haro, valido of Philip IV of Spain.

Background

Diego Fernández de Medrano y Zenizeros was the son of Diego Fernández de Medrano (likely surnamed Espinosa through maternal lineage), a Knight of the Order of Santiago, Divisoro and Lord of Sojuela, and Lord of the ancestral de la Torre and House de la Vega in La Rioja, and the Palace of Entrena. While the records do not mention a mother, the use of the surname Zenizeros appears to be hereditary; in his Heroic and Flying Fame, Diego refers to his own father as Don Diego de Medrano Zenizeros, suggesting the name was inherited through the maternal line.

Father

His fathers name appears in the divisa record of Valdeosera on 1 May 1624, along with his own. He served as commissioner of the Spanish Infantry and as Alcaide (Castellan) of the castles of Villarejo de Salvanés and Fuentidueña, both strategic fortresses of the Order of Santiago in the region of Guadalajara.

His father served the Order of Santiago at the same time as García de Medrano y Castejón, a fellow Knight of Santiago, distinguished jurist, and member of His Majesty's Councils, who authored Rules and Establishment of the Knights of Santiago (1603) and the Compilation of the Chapter Laws of the Order of Knighthood of Santiago (1605), where he made significant reforms to the laws of the Order itself.

Diego's father, Diego Fernández de Medrano, from Logroño, was the son of Captain Francisco Fernández de Medrano and Doña María Ana de Espinosa. On 1 May 1614, he and his brother Francisco Fernández de Medrano y Espinosa were formally registered as Lords of the Solar and Divisa de Regajal. A prominent figure at both court and Church, he relocated to the royal court in 1607 and went on to hold multiple prestigious positions: capellán de honor (chaplain of honor), judge of the royal chapel, administrator and deputy of the Royal Hospital of the Court, and testamentary executor to Queen Margaret of Austria.

Grandfather

Diego's grandfather was Captain Francisco Fernández de Medrano, a native of Entrena and longtime resident of Logroño. Associated with the Order of St. John, he served as Chief Magistrate (Alcalde Mayor) of the Solar de Valdeosera and as regidor of the noble estate in Logroño. Known for his valor, Francisco distinguished himself in several military campaigns and was recommended by the Duke of Savoy for the post of Alcaide of Los Arcos after sustaining serious injuries in combat at Garzigliana. Captain Francisco's brothers were Lázaro Fernández de Medrano, General Diego Fernández de Medrano, and Tomás Fernández de Medrano, Lord of Valdeosera, Secretary of State and War to the Dukes of Savoy and author of República Mista (1602), making them Diego's great-uncles. Tomás's son, Juan Fernández de Medrano y Sandoval, was also a prominent figure in the family.

Relatives

Coat of arms of the House of Medrano in Soria

Diego was born into the House of Medrano from La Rioja, one of the most distinguished noble families of royal legal officials (togados) who served the Spanish Monarchy throughout the 17th and 18th centuries. Diego Fernández de Medrano y Zezineros was connected to several high-ranking Crown officials through his extended noble lineage. Among his prominent relatives were Francisco de Medrano y Bazán, Lord of Balondo; Dr. Sebastián Francisco de Medrano; Governor Antonio Vélaz de Medrano, 1st Marquess of Tabuérniga; and García de Medrano y Álvarez de los Ríos, Lord of San Gregorio, Regent of Navarre and Seville, and a member of His Majesty’s Chamber and Royal Councils. He was also closely related to Governor Diego Fernández de Medrano y Zapata, a fellow noble of Sojuela and knight of the Order of Calatrava. The Medrano family also established themselves in Daimiel, holding positions as high mayors, governors, and chief justices of the Order of Calatrava. The Medrano family’s influence extended to Toledo, where members of the lineage served as Marshals of the Kingdom of Castile and held lordship over the towns of Caudilla and Novés.

Diego's relatives, originating from Soria and Viana, and linked to the castles of San Gregorio and Barajas in Madrid, initially settled in Ciudad Real. There, members of the Medrano family participated in the Reconquest of Alarcos in 1212 alongside Alfonso VIII of Castile at the Battle of Las Navas de Tolosa, and later served as lords of the Torre de la Galiana.

Ancestral traditions

The Medrano family is a noble house of great antiquity, recorded across different regions and periods of history. Many principles are attributed to them by authors and historians:

for its antiquity, its splendor, for their military prowess and virtue and for every other value of chivalry that prospered with this family, in great numbers, magnificent and generous.

Education

Educated at the University of Salamanca in Civil and Canon Law, the Medrano family prepared for roles as corregidores, judges, and advisors to the Crown’s Councils. Although specific academic records have not survived, Diego Fernández de Medrano y Zenizeros is described in his own works as having received an advanced education. In the dedication of his treatise Espejo de Príncipes (Mirror of Princes), he refers to himself as "Graduado de Óptimo por la floreciente Universidad de Salamanca"—a phrase indicating that he was awarded top honors from the University of Salamanca, one of the most prestigious institutions in Spain and Europe at the time. This distinction reflects a classical education grounded in philosophy, theology, and political science, consistent with his later career as a cleric, crown official, and author of political treatises. His refined Latin and eloquent Castilian prose further support his claim to scholarly distinction.

The Claustro Book of the University of Salamanca for the academic year 1668–1669 records the longstanding connection between the Medrano family and the university. For over 160 years, members of the family were affiliated with the institution—most notably the rectors and Crown officials García de Medrano y Mendizábal, I Count of Torrubia and his brother Andrés de Medrano y Mendizábal, 2nd Count of Torrubia, and Luisa de Medrano, recognized as the first female professor in both Spain and Europe.

Career

Diego Fernández de Medrano served the Church as a presbyter (priest), and also held the position of chaplain to Luis Méndez de Haro, Marquess of Carpio, valido and chief minister to King Philip IV, as well as to Pedro de Coloma, Secretary of State and member of the Royal Council of the Indies. He also served as Chief Magistrate of the Solar de Valdeosera in the years 1624–1625 and 1643–1644.

His appointment and recognition as Chief Magistrate of Valdeosera continued a family legacy: his grandfather, Captain Francisco Fernández de Medrano, had also served as Chief Magistrate in 1596, and his great-uncle Tomás Fernández de Medrano—the influential Secretary of the Dukes of Savoy—had likewise held the office in 1600 and was officially entered into the Divisa Regajal in 1589.

Estates

Diego Fernández de Medrano y Zezineros, descended from a distinguished Riojan noble line tied to the Solar de Valdeosera, one of Spain's oldest nobility collectives. Medrano held lordship over a significant collection of estates in La Rioja. He provided a condensed list that did not include all his possessions; however, based on his published works, he held the titles of Lord of the Town of Sojuela, Lord of the Solar and Divisa of Valdeosera, Lord of the Tower and House of La Vega in Rioja, and Lord of the Palace of Entrena.

Señor de la Torre and Lord of the House de la Vega in Rioja

Coat of arms of the House of de la Vega

Diego Fernández de Medrano y Zenizeros inherited not only the name but also the territorial holdings and dynastic legacy of the title Señor de la Torre y Casa de la Vega en Rioja—a noble estate tied to one of the most prominent aristocratic unions in Castilian history. This title firmly reinforced the Medrano family's place within the broader framework of High Castilian nobility.

Lord of the House of la Vega in La Rioja

Medrano's inheritance is tied to the historic union between the House of Mendoza and the House of Lasso de la Vega, established through the marriage of Leonor Lasso de la Vega to Diego Hurtado de Mendoza, Admiral of Castile. Leonor Lasso de la Vega was the daughter and only heir of Garci Lasso Ruiz de la Vega. From this marriage was born Íñigo López de Mendoza, 1st Marquess of Santillana.

Inherited through his father, by the 17th century Diego Fernández de Medrano y Zenizeros held the formal title of Señor de la Torre y Casa de la Vega en Rioja, a noble estate linked to the descendants of Garci Lasso de la Vega I. The preservation of the Casa de la Vega title—alongside the Medrano family's long-standing lordship in La Rioja—suggests that Diego inherited this hereditary estate through a cadet branch of the Lasso de la Vega lineage, likely via female-line succession.

Dynastic alliances and lineage connections

Diego Fernández de Medrano's entry into this network of noble alliances traces back to the 14th century, through Juliana de Medrano, a noblewoman of the House of Medrano, who married Juan Garcés de Almazán y Mendoza, son of Juan de Almazán and Francisca de Mendoza. Juliana made her will in Tarazona on 29 June 1371, and died shortly after, on 31 July 1371. Juan Garcés de Almazán and Juliana de Medrano were the parents of Juliana, Isabel, Hernando, and Juan de Almazán y Medrano.

Juliana de Medrano's husband's mother Francisca de Mendoza descends directly from Íñigo López de Mendoza, 1st Marquess of Santillana, son of Leonor Lasso de la Vega. Íñigo's son, Diego Hurtado de Mendoza, became the 1st Duke of the Infantado, founding one of the most powerful hereditary noble houses of Castile. The Dukes of the Infantado would go on to hold vast lands, titles, and high offices, including that of Constable of Castile.

Further dynastic ties were established through Garci Garcés de Almazán, brother-in-law of Juliana de Medrano, who married María de Tovar, heiress of the House of Tovar and relative of Juan Sancho de Tovar y Velasco, 1st Marquis of Berlanga. That house also descended from the historic union between Leonor Lasso de la Vega and Diego Hurtado de Mendoza, Admiral of Castile.

These dynastic unions—originating in Juliana de Medrano’s generation and extended through her in-laws—consolidated immense political influence and noble prestige, uniting the House of Mendoza, the House of Lasso de la Vega, and the House of Medrano into one of the most significant noble networks in medieval and early modern Spain.

The historic ties between the House of Medrano and the noble houses of de la Vega and Mendoza were reinforced in the 15th century when Diego López de Medrano (†1482), of the Soria branch of the family, was appointed Alcaide (Governor) of the Castle of Medinaceli by Luis de la Cerda y de la Vega, 1st Duke of Medinaceli and grandson of Íñigo López de Mendoza, 1st Marquis of Santillana. This appointment confirms their recognition by one of Spain’s most powerful ducal houses.

According to Luis Núñez Burillo y Ginel de Medrano, a branch of the de Medrano y Mendoza de Borbón family lineage, which included the Counts of Coruña, Dukes of Bourbon (Peers of France), Marquesses of Santillana, and Dukes of Infantado—was renowned for its academic and intellectual achievements.

Lord of Valdeosera and Sojuela

Coat of arms of the Lordship of the Valdeosera and Tejada Estate

Diego Fernández de Medrano y Zenizeros inherited the distinguished title of Lord of the Solar and Divisa of Valdeosera, a noble estate with collective lineage rights rooted in La Rioja's medieval history.

The Solar de Valdeosera was more than a title—it was a symbol of ancient nobility, deeply intertwined with regional and royal history. As Fray Juan Fernández de Medrano y Sandoval declared in 1601, the Fernández de Medrano lineage are "true and legitimate descendants" from "the field master and captain general of King Ramiro I of León," referring to Sancho Fernández de Tejada.

The collective memory of Valdeosera was further enshrined in the dedication of the Summary of the Memorable and Holy Battle of Clavijo by Salinas, where Juan Fernández de Medrano y Sandoval dedicated it to King Philip III:

This lordship will live, this memory will live, and we will live, until we die in the service of Your Majesty.

In 1601, Licenciado Salinas dedicated the prologue of the Summary of the Memorable and Holy Battle of Clavijo to Diego's great-uncle Tomás Fernández de Medrano, writing that "it seemed to me that it should be dedicated to such a principal successor." The lordship of Valdeosera and its connection to the Battle of Clavijo are noted in this passage addressed to Tomás, Lord of Valdeosera:

The lordship and lords of Valdeosera... Fernández de Medrano... having seen the archives of their antiquities and closely touched the virtue and nobility of all in general... I felt compelled to draw up a summary apart from the memorable and holy battle of Clavijo; because it is connected with the origin and antiquity of the Solar where they descend from and are lords of... for it is one of the most notable and worthy of celebration in all Spain.

Through his stewardship of Valdeosera, Diego Fernández de Medrano preserved the rights, traditions, and spiritual weight of a noble house that had been embedded in the very fabric of Castilian identity. As Lord of Valdeosera, Diego was not merely a noble by inheritance—but by example, upholding a centuries-old standard of virtue, dignity, and duty.

Recognition as Lord of Sojuela in the Solar de Valdeosera

Coat of arms of the divisa de Sojuela, La Rioja

The town of Sojuela, which Diego inherited and ruled, had been in the hands of the Fernández de Medrano family for multiple generations—through his grandfather, then father, and ultimately himself. On May 1, 1624, Diego Fernández de Medrano, Lord of Valdeosera, was formally recorded in the Divisa Regajal of the Solar de Valdeosera, a noble lineage estate in La Rioja. The registry entry notes that he and his father Diego Fernández de Medrano were entered together in the official book, with the younger Diego recognized on page 109 as Lord of the town of Sojuela. This inscription affirmed the family's hereditary rights and noble status within the historic collective of the Thirteen Divisas, further solidifying their social and territorial authority in the region.

Sojuela

Located near the capital, Logroño, Sojuela belonged to a network of settlements known as the Villas de Campo, situated in the Iregua River valley. Its historical importance stemmed from its association with the Monastery of San Julián de Sojuela, which served as a central hub for regional repopulation efforts. In 1060, Stephanie, Queen of Navarre, widow of King García Sánchez III of Pamplona, issued a fuero (charter) to San Vicente de Sojuela and neighboring villages like Medrano, Entrena, and Fuenmayor, all under the jurisdiction of the ancient Medrano family. This document outlined their duties to the Monastery of San Julián, establishing it as the primary governing and spiritual authority in the area.

Works

Heroic and Flying Fame of the Most Excellent Don Luis Mendez de Haro by Diego Fernandez de Medrano, Lord of Sojuela and Valdeosera

Diego Fernández de Medrano y Zenizeros is best remembered continuing the family tradition, producing two literary works: a mirror for princes-style treatise addressed to Prince Philip Prospero, and a soaring panegyric dedicated to the valido Luis Méndez de Haro. Medrano's rhetorical style blends classical allusion with deeply personal loyalty, casting statesmanship in almost sacred terms.

Fama heroica y voladora (Heroic and Flying Fame)

Portrait of Luis Méndez de Haro y Guzmán by Cornelis Meyssens

His work Heroic and Flying Fame of the Most Excellent Lord Don Luis Méndez de Haro, Count-Duke of Olivares—the Pillar upon which rests the Majesty of Philip IV of Spain and the weight of government of his kingdoms, etc is a hybrid of panegyric and political treatise. It was dedicated to Pedro Coloma, Secretary of State and confidant of the Crown, under whom Medrano also served as chaplain.

The work praises Luis Méndez de Haro, chief minister to King Philip IV, portraying him as the ideal royal favorite (valido) and restorer of Spanish honor following the decline of his predecessor, the Count-Duke of Olivares. More than a courtly eulogy, it offers a political commentary on statecraft, meritocracy, and virtuous leadership. Using allegory and classical allusion, Medrano casts Haro as both a savior of the monarchy and a paragon of virtue—showing how personal morality and good governance must go hand in hand.

Dedication to Pedro Coloma

In his dedication to Secretary of State Pedro Coloma, Medrano extols Luis Méndez de Haro not merely as a statesman but as a figure of almost mythical stature—"the Archpolitician of the World"—whose accomplishments transcend ordinary praise. He declares that Haro's deeds were "not deserving of fragile statues of stone, but of bronze that would make his fame immortal," evoking a timeless image of political virtue cast in permanence. For Medrano, Haro's orchestration of peace between Spain and France (Treaty of the Pyrenees) is more than diplomacy; it is a divine act:

No imaginable consideration could explain this better… for he has so faithfully served Divine Majesty... the general remedy of the world consists in the universal peace and concord of the Christian princes.

Luis Méndez de Haro

Medrano positions Haro within the pantheon of classical greatness, only to elevate him above it: "Neither Aristotle could discourse, nor Euclid measure, nor Apelles paint the Prince with attentiveness… as did the Most Excellent Lord Don Luis Méndez de Haro." These comparisons are not mere literary flourishes but calculated affirmations of the valido's unmatched balance of intellect, justice, and statesmanship. Writing not only as a loyal subject but as Haro's chaplain, Medrano reflects personally on the debt he and his father Diego de Medrano (a Knight of Santiago) owe to their patron:

Oh, if my pen could match the wings of his fame… for it has come so close to his recognition: a small satisfaction, scant acknowledgment of the honors, favors, and courtesies…

His words are written with reverence and a sense of near-religious devotion, turning political service into a sacred obligation. Ultimately, Medrano frames Haro's legacy as world-shaping and salvific in scope, a final chord of theological and geopolitical harmony.

Espejo de príncipes (Mirror of Princes)

Diego Fernández de Medrano y Zenizeros authored Espejo de príncipes: Crisol de sus virtudes, asombro de sus fealdades, alma de su gobierno y gobierno de su alma ("Mirror of Princes: Crucible of their Virtues, Astonishment of their Failings, Soul of their Government and Government of their Soul"), a moral-political treatise addressed to Prince Philip Prospero, heir to the Spanish throne:

Sir, Academies have always been the courts of princes—adorned, instructed, and refined in the liberal science of governance. It was for such a purpose that they were established, and with even greater care, those that succeeded took shape. Throughout Europe, political restoration has always been initiated—or at least illuminated—by men of great judgment, who provided to noble assemblies the first precepts of nature, placing above political laws the laws of the Catholic faith.

My own conviction has always been firm: that true authority must be grounded in Christian truth and defended with the pen, the sword, and the soul—through divine demonstrations. When doctrines of greater gravity were needed to instruct a prince, it was always the Spanish who were most blessed with such enlightenment. They are the reflection of the House of Austria—the Philips—beginning with the first who brought to Hispania a noble Caesar and a symbolic fortress that gave to Castile and León a second Philip, whose legacy of goodness and fame was confirmed in a second.

And now, Heaven bestows upon Your Highness, for the joy of Spain and as a reward for your parents’ charity, a Prince whose admirable qualities already promise that he shall succeed with his own virtues. In him, authority shall shine, and under his just name and single person, the glory of princes across the world shall be adorned.

Summary of Mirror of Princes

Diego Fernández de Medrano y Zenizeros was the author of Espejo de Príncipes: Crisol de sus Virtudes, Asombro de sus Fealdades, Alma de su Gobierno y Gobierno de su Alma ("Mirror of Princes: Crucible of their Virtues, Astonishment of their Failings, Soul of their Government and Government of their Soul"), a political-moral treatise composed between 1657 and 1661 and dedicated to Prince Philip Prospero of Spain.

Divided into 29 discourses and a concluding oration, the work stages a fictional tribunal in which Reason judges a parade of emperors, kings, and statesmen, exposing their vices and exalting their virtues. Opening with an epistle to the reader, Diego presents the work as a confrontation between a ruler’s inner conscience and the uncompromising realities of power. He warns that "truth is the mirror of princes," and that leaders must reflect virtue. If the reflection is harsh, the blame lies not with the mirror—but with the flaws it reveals.

Rulers such as Augustus, Julius Caesar, Trajan, Alexander the Great, and Marcus Aurelius are summoned and commended for their wisdom, military discipline, and moral restraint. In contrast, figures like Nero, Caligula, Tiberius, Galba, and Commodus are held accountable for cruelty, hedonism, or cowardice. Among the most climactic moments is the rehabilitation of Emperor Otho, who is praised for taking his own life to prevent civil war—an act Diego portrays as sacrificial and republican in spirit (patria).

The treatise does not limit itself to ancient history. In Discourse Nineteen, Diego references Francisco de Quevedo, the renowned Spanish Baroque writer who attended the Medrano Academy, quoting him directly: "Who governs himself well, governs well the Republic." This interjection of contemporary wisdom reinforces the broader aim of the text—to mold not just rulers of the past, but to guide the education and virtue of future princes.

The final Oration directly addresses Prince Philip Prospero, urging him to contemplate the examples laid before him and become a prince "whose soul governs the state, and whose state elevates the soul." In this way, Espejo de Príncipes becomes both a mirror and a guidebook—rooted in classical precedent, infused with Spanish political thought, and reflective of the Medrano family's enduring intellectual tradition.

Through literary allegory and scriptural citations, Medrano constructs a mirror in which rulers may see both their ideal form and potential downfall. Mirror of Princes synthesizes Medrano’s political philosophy, portraying the prince as both subject to divine order and responsible for the moral welfare of the state. Intended as both admonition and guidebook, the Espejo de Príncipes encapsulates the culmination of Medrano’s service to monarchy and Church, and reflects the deeply moralized vision of political power characteristic of Spanish baroque thought. It is one of the few surviving Iberian contributions to the "mirror for princes" genre during the late Spanish Habsburg era.

Epistle

In his epistle, Diego Fernández de Medrano writes directly to the reader:

A mirror is not for flattery, as the courtly often use it. The mirror is faithful: to faults it gives proportioned truth. It does not only reflect what is clear, but all that is within. A broken mirror is the mirror of deceit, and that is no mirror at all—just a lie. Truth is the mirror of princes, and princes should be mirrors of virtue. There is no better mirror than reason, nor any more perfect than that which reflects virtue with clarity and action. There is no mirror that should be used more than this one, nor one more justly esteemed by those guided by reason. Though there are mirrors that reflect what the deceivers wish to see, the mirror that shows a prince or a nobleman how to govern rightly is the mirror of reason. This mirror, although made of hard metal, aims to reflect clearly. If anyone finds it too sharp, let him not accuse the mirror, but rather acknowledge the faults that it reflects. For it is the guilty who find fault in the mirror’s truth. I present it not to praise particular individuals, nor out of vanity, but to describe as a painter might, and to offer a sketch and report of my intent. 'Let it be a mirror to all kings, princes, and great men, to guide them in virtue and expose them to their failings, so that all may learn: as many as are adorned by their virtues, and as many as are darkened by their vices. Let them see their image—and rise.' Vale (Farewell).

Modern analysis

In a posthumous tribute to the renowned philologist Germà Colón, scholar Santiago Fortuño Llorens analyzed Espejo de príncipes, a work by Diego Fernández de Medrano y Zenizeros, exploring its literary connections to the style and thought of Francisco de Quevedo. This study was part of a broader volume showcasing medieval and Golden Age literature, and reflected Colón’s lasting influence on academic research in Romance studies.

Continuation of the República Mista doctrine

República Mista (1602) by Tomás Fernández de Medrano.

Diego's great-uncle, Tomás Fernández de Medrano, Lord of Valdeosera, articulated a vision of the prudent and virtuous valido during the reign of Philip III of Spain. In his 1602 treatise República Mista, Tomás championed the valido (royal favorite) not as a threat to royal authority but an extension of the sovereign’s will, insisting that a ruler's ministers shape the moral fabric of the republic more powerfully than laws alone.

A generation later, Diego carried this doctrine forward. In his panegyric-treatise Heroic and Flying Fame, Diego exalts Haro—nephew and successor to the Count-Duke of Olivares—as an ideal valido whose wisdom, moderation, and Christian virtue restored both Spain's reputation and God's favor. Together, Tomás and Diego present a unified Medrano philosophy: that wise and temperate royal delegation, far from undermining monarchy, represents its highest refinement. In Diego's hands, the valido becomes not only a tool of effective statecraft but a "vessel of divine and political harmony," and the prince is trained to embody virtue, restraint, and discernment in power.

This political vision is further complemented by Diego’s more didactic treatise, Mirror of Princes: Crucible of their Virtues, Astonishment of their Failings, Soul of their Government and Government of their Soul (Spanish: Espejo de príncipes: Crisol de sus virtudes...) written for Prince Philip Prospero.

Together, Diego’s treatises serve as both a reaffirmation and a culmination of the doctrine first articulated in República Mista, reflecting the Medrano family's enduring intellectual contribution to the theory and practice of royal delegation and moral governance rooted in divine and natural law at the height of Spanish Habsburg rule.