Has a slave served as a priest?

In a recent sermon on Ephesians 6.5-9, the possibility was raised of a slave being a priest/pastor/bishop with authority over his earthly master. I couldn't think of an example from Church history. What examples are there in Church History (ancient or modern) of a priest or equivalent who was a slave at the time of their serving? Also, are there relevant canons (Roman or Orthodox) about this situation?