Cedric

Cedric is a man wh curries favor with Arthur, replacing Merlin as his manservant so that he can then steal a beautiful jewel found in a tomb underneath Camelot.

However, the jewel actually contains the soul of Cornelius Sigan, a powerful and evil sorcerer in Camelot's past, and Cedric is possessed by him. He later died (presumably) along with Sigan after Merlin enlists the help of Kilgharrah to end Sigans' threat to Camelot.