(1578-1621) king of Spain from 1598, the son and successor of Philip II by his fourth and last marriage. An introspective and deeply religious man, he left government to corrupt ministers and devoted himself to the interests of the church. During his reign, agriculture and industry declined, and foreign wars drained the treasury. In 1606 the Moriscos (Muslim converts to Christianity) were expelled from Spain. He was married to Margaret of Austria
(1584-1611), grand-niece of Charles V
. He was succeeded by his son Philip IV. See: Diego Velázquez. Queen Margarita on Horseback.