Potiphar is Joseph's first boss once he's sold into slavery. He's one of Pharaoh's officials, the captain of the guard. He can't say enough about Joseph, or give him enough responsibility, practically handing over the keys to the castle.
Potiphar's fatal flaw is that he trusts his wife, and she's no Helen. Nope—this one's a seductress, and she lands Joseph in jail when he won't take the bait (39:19-20).