King of Castile and León (1350–1369) whose bitter civil war against his illegitimate half-brothers ended with his murder by Henry of Trastámara, opening the Trastámara dynasty.
Peter of Castile, remembered by his enemies as "the Cruel" and by his partisans as "the Just", was king of Castile and León from 1350 to 1369. His reign was consumed by a ferocious civil war against his illegitimate half-brothers, the sons of Alfonso XI by Leonor de Guzmán, led by Henry of Trastámara.
The struggle became a front of the Hundred Years' War, with Peter allied to England and the Black Prince and Henry to France. After early victory, Peter was finally defeated and murdered by Henry at Montiel in 1369, an act that ended the old Castilian line and founded the Trastámara dynasty.
Peter was born in 1334, the legitimate son and heir of Alfonso XI of Castile. His father, however, openly favoured his mistress Leonor de Guzmán and their many sons, and on Alfonso's death in 1350 the rivalry between Peter and these half-brothers — above all Henry of Trastámara — set the pattern for his whole reign.
Peter came to the throne as a teenager under the influence of the powerful courtier Juan Alfonso de Alburquerque, and his early attempts to assert royal authority against the great nobles quickly hardened into the violence that gave him his byname.
Peter's reputation is one of the most contested of any medieval king, because the sources that shaped it were written by his enemies. The chronicle of Pero López de Ayala, composed under the victorious Trastámara dynasty, fixed the image of "Peter the Cruel": a vengeful, suspicious king who had opponents, kinsmen, and his own French wife Blanche of Bourbon killed.
A rival tradition remembered him as "the Just" (el Justiciero), a king who enforced royal law harshly against overmighty nobles and protected townspeople and the vulnerable. The truth is hard to recover beneath the propaganda of the dynasty that overthrew him, but both traditions agree on a ruler of fierce will and readiness for violence, whose reign was defined by the merciless logic of a civil war for survival.
Peter's reign was dominated by the war against Henry of Trastámara and his brothers. The conflict drew in the great powers: Henry was backed by France and the Aragonese and by the Breton captain Bertrand du Guesclin, while Peter allied with Edward, the Black Prince, and England. In 1367 the Black Prince won a crushing victory for Peter at the Battle of Nájera, temporarily restoring him.
The English alliance did not hold. When the Black Prince withdrew, unpaid and disillusioned, Henry returned with French support. In 1369 Peter was besieged and defeated at Montiel; lured to a parley in his half-brother's tent, he was seized and stabbed to death by Henry himself.
Peter was killed at Montiel on 23 March 1369 in a personal struggle with Henry of Trastámara, who thereby made himself king as Henry II. Peter's death ended the direct line of the old Castilian royal house and transferred the crown to the illegitimate Trastámara branch.
Peter of Castile is remembered as much for his contested reputation as for his reign: the "Cruel" of Trastámara propaganda and the "Just" of a counter-tradition. His murder founded the Trastámara dynasty that would rule Castile — and, through his descendants, unite it with Aragon under the Catholic Monarchs. His entanglement of the Castilian civil war with the Hundred Years' War also marks how deeply Iberian and wider European conflicts had become linked by the fourteenth century.