Moses the Black

The power of repentance has transformed this infidel slave, St. Moses the Black (330-405 A.D.), who was a murderer, adulterer and robber into a great Desert Father, teacher, comforter, and priest , who wrote rules for the monks , and a martyr -saint whose name continues to be mentioned on the altar and in our prayers.
His feast day is on August 28 .

Source: OrthodoxWiki