Arsenios Autoreianos (Latinized as Arsenius Autorianus) (Greek: Ἀρσένιος Ἀυτωρειανός) (ca. 1200 – 1273), Ecumenical Patriarch of Constantinople, lived about the middle of the 13th century.
Born in Constantinople ca. 1200, Arsenios received his education in Nicaea at a monastery of which he later became the abbot, though not in orders. Subsequently he gave himself up to a life of solitary asceticism in a Bithynian monastery, and is said, probably wrongly, to have remained some time in a monastery on Mount Athos.
From this seclusion he was called by the Byzantine Emperor Theodore II Lascaris to the position of patriarch at Nicaea in 1255. Upon the emperor's death Arsenios may have shared guardianship of his son John IV Lascaris with George Muzalon: while the later historians Nikephoros Gregoras and Makarios Melissenos say the Patriarch was so named, the contemporary historians Pachymeres and Acropolites name only Mouzalon. Nevertheless, a few days after Theodore's death George Muzalon was murdered by Michael Palaiologos, and who, at an assembly of the aristocracy presided over by Patriarch Arsenios, was appointed regent for the boy. Arsenios also performed the double coronation of Michael Palaiologos and John Lascaris in January 1259.
Through the time between the death of Mouzalon and the double coronation, Arsenios had worked to protect the rights of the young emperor John Lascaris, at one point insisting that John and Michael exchange mutual oaths of loyalty. He also insisted that at the double coronation John Lascaris should be crowned first, which Michael Palaiologos saw as a serious barrier to his final usurpation. Pressure was put upon the patriarch to allow Palaiologos to be crowned alone, and even the young emperor was threatened. The patriarch found no support from the bishops assembled: except for two prelates, all believed that Palaiologos had the right to be crowned first. Arsenios at last conceded the point and crowned Michael and his wife first, while John Lascaris received only a special head-dress.