With Great Knowledge comes Great Responsibility.. In the Star Wars comics there are evil versions on C-3PO and R2-D2. They are called 0-0-0 or Triple Zero and BT-1. They not only look alike, but they go out of their way to cause death and destruction while C-3PO and R2-D2 are always on the lookout to help the humans around them.
After being found and reactivated by Doctor Aphra, BT-1 and his fellow droid 0-0-0 served under Lord Vader, and when Aphra faked her own death, he and 0-0-0 continued to roam the galaxy with her.