Peter IV (Peter the Ceremonious), 1319?–1387, king of Aragón and count of Barcelona (1336–87); son and successor of Alfonso IV. He supported Alfonso XI of Castile at the battle of Tarifa (1340), recovered (1343–44) the kingdom of Majorca, and engaged in an indecisive naval war with Genoa and Pisa over possession of Sardinia. Though forced to confirm the privileges granted to the nobles by Alfonso III, Peter later (1348) defeated the troops of the nobles and withdrew their charter. In 1381 he assumed suzerainty over the duchy of Athens. His son, John I, succeeded him.

Peter IV, king of Portugal: see Pedro I, emperor of Brazil.