The butler? You mean C3PO? Of course he did it. No one suspects the robot but he's been on the dark side since the beginning. I mean, you can tell everyone that negative feeling, fears and so on, lead to the dark side, and then show them a robot afraid of everything, and they'll say, omg did you hear about Luke, Leia, Vader, anyone but the damn robot right in front of their eyes?!?!
Darth 3PO. The one they never suspect.