Athanasius I of Constantinople was a Byzantine prelate who served as the Ecumenical Patriarch during two separate periods between 1289 and 1309. Born in Edirne around 1230, he was appointed to the position by Emperor Andronikos II Palaiologos. His leadership was defined by his resistance to the unification of the Greek and Roman churches and his attempts to implement ecclesiastical reforms. Although he faced significant clerical opposition, he regained his office in 1303 through the support of the people.