King Peter IV of Aragon, also known as Peter the Ceremonious, ruled from 1336 to 1387. He was a member of the House of Barcelona and played a significant role in the political landscape of Aragon during the late Middle Ages. His reign was marked by efforts to strengthen the monarchy and expand the kingdom's influence. Peter IV is known for his legal reforms and the establishment of the Cortes of Aragon, which allowed for greater representation of the nobility and townspeople. He also faced challenges, including conflicts with the Crown of Castile and internal strife, but he successfully maintained Aragon's independence and territorial integrity.