Mark Sheppard is a British actor, probably best known to American audiences as Crowley on Supernatural or Jim Sterling on Leverage. His first role in a major production was a supporting one for In the Name of the Father (1993), and since then he has popped up all over the place, including the short-lived Firefly. He and his father, William Morgan Sheppard, are the only father-son pair to have both (though separately as the same character) appeared on Doctor Who.
On Warehouse 13, he portrays Benedict Valda, a Regent.