Morgana Pendragon

Morgana started the series off by being a sweet, kind-hearted girl, who loved people and always did what her heart told her. She is the beautiful ward of King Uther Pendragon. She finds out that she has magic, and fears for her life, because Uther kills anyone with it. She turns against Camalot, and for a long time no one knows except Merlin and Gaius, but at the end of the third series she shows her true colours, and driver Uther to madness.

all through the 4th and 5th series she is plotting the demise of Arthur and Camalot, and in the final episode, when Arthur is dying, Merlin stabs her with Excalibur, and he holds her as she dies.