Peter II of Aragon (1174 - September 12 1213), surnamed the Catholic, was the king of Aragon (as Pedro II) and count of Barcelona (as Pere I) from 1196 to 1213.

He was the son of Alfonso II of Aragon and Sancha of Castile. In 1205 he acknowledged the feudal supremacy of the Papacy and was crowned in Rome by Pope Innocent III, swearing to defend the Catholic faith (hence his surname, "the Catholic"). He was the first king of Aragon to be crowned by the Pope.

On June 15, 1204 he married (as her third husband) Marie of Montpellier , daughter and heiress of William VIII of Montpellier . She gave him a son, James, but Peter soon discarded her. Marie was popularly venerated as a saint for her piety and marital suffering, but was never canonized; she died in Rome in 1213.

He led the Christian forces to defeat the Moors at the Battle of Las Navas de Tolosa in 1212.

Ironically, the Catholic king died in September 12 1213 at the Battle of Muret , trying to defend his vassal and brother-in-law, count Raymond VI of Toulouse, against the crusaders of Simon de Montfort, 5th Earl of Leicester. (see Albigensian Crusade)