Peter I (Basque: Petri I.a Sanoitz) was the King of Aragon and Navarre for a decade from 1094 until his death. He was the son and successor of Sancho V Ramírez by his first wife, Isabella of Urgell. He was named in honour of Saint Peter, because of his father's special devotion to the Holy See, to which he had made his kingdom a vassal.
Peter continued his father's close alliance with the Church and pursued his military thrust south against bordering Al-Andalus taifas with great success, allying with Rodrigo Díaz de Vivar, known as El Cid, the ruler of Valencia, against the Almoravids. According to the medieval Annales Compostellani Peter was "in bellis expertus et audax in principio" (expert in war and daring in initiative), and one modern historian has remarked that "his grasp of the possibilities inherent in the age seems to have been faultless."
When Peter I died in the Val d'Aran, his kingdoms passed to his younger half-brother, Alfonso the Battler. Peter was buried in San Juan de la Peña alongside his children. When Alfonso also died without living children, the kingdom of Aragon passed to the youngest brother, Ramiro II. Peter's name was adopted, in a feminised form, for Ramiro's only child, and successor, Petronilla (1037–64). The name Peter entered the name pool of the House of Barcelona into which Petronilla married and was thereafter common in the ruling family of Aragon.