Achillas of Alexandria was an early Christian leader who served as the 18th Patriarch of Alexandria from 312 to 313. Born in Alexandria, he was a highly respected priest and the head of the city's Catechetical School. Known for his deep understanding of theology and Greek philosophy, he was later honored by Athanasius as "Achillas the Great." He ascended to the patriarchate following the death of Pope Peter during the Diocletianic Persecution.