From relatively humble beginnings in Medina del Campo, where he studied grammar, he took advantage of a secular custom of Castilian monarchs to selectively promote lower class court nobility to the service of Ferdinand I of Aragon—a privilege normally reserved for those of high birth.

It is probable, though not possible to conclusively demonstrate, that his family were originally Marranos—that is, Sephardic Jews who in earlier times adopted the identity of Christians, either by sincere conversion or through coercion, or who, for form's sake, became Catholic converts in service to the Crown.

Barrientos and Torquemada had many things in common: they were both likely of Jewish origin; belonged to the Dominican Order; came from villages in the province of Valladolid; and, undoubtedly, shared ideas on the religious problem of Castile.

Being loyal to John II, in 1442 he reformed the diocese of Segovia, which had been under the influence of the rebellious prince Henry, to serve the province of Ávila in supporting the King.

Similarly, in 1449, he pledged the arms of the diocese in defense against the troops of don Alonso de Aragón and other Castilian noblemen who opposed the king.

At the end of the 15th century, a wide sector of Spanish society was hostile toward Jews; as the Franciscan, Alphonso de Spina explains in his treatise, Fortalitium Fidei: "Entraron, ¡oh Señor!, en tu rebaño los lobos rapaces.

Nadie piensa en los pérfidos judíos, que blasfeman de tu nombre" (They entered your flock, oh Lord!, as greedy wolves.

[2] Barrientos wrote a number of tracts defending Jews; in one he recognized that it is "posible es que aya algunos, pero puesto que ansy sea, injusta e inhumana cosa sería todo el linaje dellos manzellar nin diffamar" (possible that there are some deserving of condemnation, but even if that is the case, it would be unjust and cruel to debase and defame all people of Jewish heritage).

In 1449 he obtained a favorable response; according to Barrientos, the Pontiff "había mandado que no se hiciera ninguna discriminación entre los nuevos convertidos a la fe y los cristianos viejos en la recepción y tenencia de honores, dignidades y oficios, tanto eclesiásticos como seculares" (ordered him not to discriminate between new converts to the faith and old Christians in the reception and tenancy of honors, dignities and offices, both ecclesiastical and secular).

They defended this ideology until Tomás de Torquemada, the grand inquisitor, convinced Isabella I of Castile and Ferdinand II of Aragon to act.

Villena was a man of letters who wrote on diverse topics, was a translator (most notably of Virgil's Aeneid), a surgeon, and it is possible that he collected books in Hebrew and Arabic; such pursuits automatically turned him into a suspected heretic.

Although John II was himself a man of innovative ideas and one of the more cultured people of his age, like many of the era, he distrusted intellectuals, and, in response to Barrientos' suit, condemned Enrique de Villena to prison.

These events are well attested in unpublished works authored by Barrientos, which still exist in Salamanca, such as his Tratado de caso e fortuna (Treatise on Prophesies).

[6] The poet, Juan de Mena (1411–1456), a chronicler of King John II's life, skewered Barrientos for these deeds in his Laberinto de fortuna ("Labyrinth of Fortune"), a 300-octave poem which explicitly mirrors the form of Dante Alighieri's Divine Comedy:[7] Some accused Barrientos of being a savage and of plundering the most valuable books in Villena's collection in order to plagiarize them.

While this is praiseworthy, on the other hand, it is useful to entrust some books to reliable people who would use them solely with the goal of educating themselves to better defend the Christian religion and faith and to bedevil idolaters and practitioners of necromancy.

Nevertheless, everything points to the fact that he betrayed his monarch; when John II was celebrating, believing himself to be secure in the heart of Medina del Campo, troops of the Kingdom of Navarre burst into the villa where he was sheltering and took him prisoner.

Although John II of Aragon had continued to occupy the region, consolidating his annexation, the death of his wife, Blanca de Navarra, forced him to leave the Castilian campaign and beat a hasty retreat home, as his own crown was in danger from the pretensions of his stepson, Charles of Viana.

In a fit of pique, led by the city's chief warder, Pedro Sarmiento, who had for years sought to expel Toledo's converted Jews, several high-ranking tax collectors of Jewish extraction were executed.

Barrientos scoffed at Henry for his failure to act in the face of rumors impugning his character, such as the infidelity of the queen with one of his confidants, and talk of his homosexuality.

Because the majority of Lope de Barrientos' writings are of a theological bent and addressed to issues of his era, they are more the province of scholarly study today, than of general interest.

[13] John II of Castile bestowed on Barrientos the dominions of Pascualcobo and Serranos de la Torre in Ávila, on which he built a number of estates in diverse towns.