Henry IV of Castile was a king who ruled from 1454 to 1474 in the Kingdom of Castile, part of modern-day Spain. He was born in 1425 and was the son of John II of Castile and Maria of Aragon. His reign was marked by political instability, conflicts with the nobility, and challenges to his legitimacy, including disputes over his marriage and the succession of the throne. Henry IV is often remembered for his attempts to strengthen royal authority and his efforts to manage the powerful noble families of Castile. His reign ended with his death in 1474, leading to a succession crisis that ultimately contributed to the rise of Isabella I of Castile and Ferdinand II of Aragon, who would unite Spain.