Alexander of Constantinople was a 4th-century prelate who served as the bishop of Byzantium starting in 314. He became the first bishop of Constantinople following the city's renaming in 330. Originally from Calabria, he was noted for his administrative skills and his defense of orthodoxy. During the Arian controversy, he famously refused to restore Arius to communion, fearing the heretic's repentance was insincere, a stance he maintained despite threats of deposition from imperial supporters.