Pope Alexander I of Alexandria

Alexander I of Alexandria (Koine Greek: Ἀλέξανδρος, Aléxandros) was the 19th Patriarch of Alexandria.

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 mentored his successor, Athanasius of Alexandria, who would become an important Church Father and advocate of the Nicene position against the Arians. He is venerated as a saint in the Catholic and Orthodox Churches.

Source: Wikipedia — https://en.wikipedia.org/wiki/Pope_Alexander_I_of_Alexandria