Ramiro II of Aragon

Ramiro II (24 April 1086 – 16 August 1157), called the Monk, was a member of the House of Jiménez who became King of Aragon in 1134. Although a monk, he was elected by the Aragonese nobility to succeed his childless brother Alfonso the Battler. He then had a daughter, Petronilla, whom he had marry Count Ramon Berenguer IV of Barcelona, unifying Aragon and Barcelona into the Crown of Aragon. He withdrew to a monastery in 1137, leaving authority to Ramon Berenguer but keeping the royal title until his death.

Source: Wikipedia — https://en.wikipedia.org/wiki/Ramiro_II_of_Aragon