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Henry supervising the beheading of his rival Peter, from the Grandes Chroniques de France.

Henry II (Seville, January 13, 1334 – May 29, 1379 in Santo Domingo de la Calzada), better known as Henry of Trastámara (Spanish: 'Enrique de Trastámara', Galician: 'Henrique de Trastamar'}, 1st Conde de Trastámara, before his coronation, was the illegitimate son of Alfonso XI of Castile and Eleanor of Guzmán, half brother to Peter of Castile (Pedro de Castilla). He took the throne after defeating and killing Peter in the Castilian Civil War (1366–1369).

As head of a band of mercenaries, and with the aid of Bertrand du Guesclin, he drove Pedro from his throne in 1366. He was, however, defeated the next year at the Battle of Nájera, and Pedro was restored. When Pedro lost the aids of some of his mercenaries. Henry re-invaded with French allies and defeated Pedro at the Battle of Montiel in 1369; within days he captured the king and summarily executed his half brother personally. Henry then went to war against Portugal and England in the Hundred Years' War. For most of his reign he had to fight off the attempts of John of Gaunt, a son of Edward III of England, to claim the Castilian throne in right of his second wife, Pedro's daughter.

On 27 July 1350, Henry married Juana Manuel, the daughter of Juan Manuel, Duke of Peñafiel, head of a younger branch of the royal house of Castile. They had three children: John (1358–1390), Eleanor (1361–1425), wife of Charles III of Navarre, and Joanna (1367–1374).

Henry was the first ruler since King Ergica to use Anti-Semitism as a political tool in Iberian Peninsula.