Pope Alexander of Alexandria, 19th Pope of Alexandria & Patriarch of the See of St. Mark. During his patriarchate, he dealt with a number of issues facing the Church in that day. These included the dating of Easter, the actions of Meletius of Lycopolis, and the issue of greatest substance, Arianism. He was the leader of the opposition to Arianism at the First Council of Nicaea. He also is remembered for being the mentor of the man who would be his successor, Athanasius of Alexandria, who would become one of the leading Church fathers.