chief minister and favourite of King Philip IV (reigned 1621–65), who failed to stem the decline of Spanish power and prestige.

Haro's political career advanced under the patronage of his uncle Gaspar Olivares (Olivares, Gaspar de Guzmán y Pimental, conde-duque de, duque de Sanlúcar de Barrameda), who was chief minister during 1621–43 and whom he succeeded when Olivares fell from favour. Shortly thereafter the era of Spanish military preeminence ended with the defeat at the Battle of Rocroi (Rocroi, Battle of) (May 1643). Haro was able to claim success in the suppression of rebellion in Spain's Italian possessions, but he could not arrest economic decline and consequent social distress. He also failed to subdue the rebellious Portuguese or stem English colonial encroachments. Haro gained moderate terms in the Peace of the Pyrenees (Pyrenees, Peace of the) (1659), which ended the long war with France; nevertheless, Spanish power was on the wane.