Henry III (October 4, 1379 — 1406), sometimes known as Henry the Sufferer or Henry the Infirm (Spanish: Enrique el Doliente) was the son of John I and succeeded him as King of Castile and León in 1390.

Henry was born in Burgos, the capital of Castile. Before becoming king, he was known by the title Prince of Asturias, designating him as the heir apparent. After succeeding to the throne at 11, Henry took power at 14. He was able to pacify the nobility and restore royal power. During his reign, the Castilian fleet won several victories against the English; Henry sent a naval fleet in 1400 that destroyed Tétouan in North Africa, a pirate base. In 1402, Henry began the colonization of the Canary Islands, sending French explorer Jean de Béthencourt. He also sent envoys to Timur.

Henry married Catherine of Lancaster (1372-1418; Spanish: Catalina), the daughter of John of Gaunt, in 1388. This ended a dynastic conflict and solidified the House of Trastamara. After Catherine's death, Henry married Constance (1372-1418; Spanish: Constanza) the daughter of Peter I. Their son became John II of Castile, who succeeded Henry when he died in Toledo.