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?
Has a slave served as a priest?

Geremia does a great job in demonstrating that a being a slave is a serious impediment to being ordained.

Nevertheless the Church does have examples of ex-slaves being ordained priests and even consecrated bishops and eventually canonized a saint. The following are a few examples:


St. Patrick 
Servant of God, Fr. Augustus Tolton


There is saint who vowed to become a slave of slaves:


St. Peter Claver, Apostle of Slaves


There are Religious Orders for the redemption and freedom of slaves:


Order of the Blessed Virgin Mary of Mercy
Order of the Most Holy Trinity for the Redemption of Captives


However according to the Orthodox, St. Paulinus volunteered to become a slave by taking the place of another:


  When the Vandal barbarians invaded Italy and carried off many people to Africa in captivity, Saint Paulinus used church funds to ransom the captives. However, he did not have enough money to ransom the son of a certain poor widow from slavery in the household of the Prince of the Vandals. So, he volunteered to take his place. Dressed as a slave, Saint Paulinus began to serve the Vandal prince as a gardener. - St. Paulinus the Merciful the Bishop of Nola


St. Paulinus of Nola is also a saint in the Catholic Church. However Wikipedia makes this story a legend:


  Gregory the Great recounts a popular story that alleges that when the Vandals raided Campania, a poor widow came to Paulinus for help when her only son had been carried off by the son-in-law of the Vandal king. Having exhausted his resources in ransoming other captives, Paulinus said, "Such as I have I give thee", and went to Africa to exchange places with the widow's son. There Paulinus was accepted in place of the widow's son, and employed as gardener. After a time the king found out that his son-in-law's slave was the great Bishop of Nola. He at once set him free, granting him also the freedom of all the captive townsmen of Nola. According to Pope Benedict XVI, "...the historical truth of this episode is disputed, but the figure of a Bishop with a great heart who knew how to make himself close to his people in the sorrowful trials of the barbarian invasions lives on."