Arsenios Autoreianos was a 13th-century Eastern Orthodox prelate who served as the Ecumenical Patriarch of Constantinople. Born in Constantinople around 1200, he received his education at a monastery in Nicaea and spent time living as a solitary ascetic. He rose to prominence when he was appointed Patriarch of Nicaea in 1255, eventually acting as a co-regent for the young emperor John IV Laskaris. His leadership was defined by his firm commitment to ecclesiastical discipline and his resistance to imperial interference in church matters.