Which 4th-century Egyptian saint was a former slave and gang leader before becoming a monk?

The 4th-century Egyptian saint who was a former slave and gang leader before becoming a monk was Moses the Black.

Also called Moses the Ethiopian, Moses the Strong, or Moses the Robber, he was a Nubian ascetic associated with Scetis, a major monastic center in Egypt. Traditional accounts say that after his master expelled him for murder, Moses joined a violent band of robbers and eventually became its leader.

His conversion began after he encountered monks in the desert. Their disciplined, peaceful life affected him so deeply that he was baptized, entered the monastic community, and gradually became a respected spiritual teacher. He was later ordained a priest and led a group of hermits.

A common mix-up is with Moses of the Bible, who led the Israelites out of Egypt. Moses the Black was a much later Christian Desert Father. Tradition also remembers him for rejecting violence: when raiders threatened his monastery, he refused to fight and was killed with several other monks around 405.