Bolog

Bolog was a villain who once concealed the whole Reptilios Invasion Fleet on the dark side of the Moon in order to conquer the Earth. But the Doctor, helped by Romana and K9, sent the Fleet into orbit using a banana.

Some time later, Bolog joined forces with several aliens to try to kill the Doctor, their common enemy. He shot Questor in the face, believing him to be the Doctor in disguise.

Later caught in a triangular gunshot, he was shot by the alien known as "The Pernicious Profligate Plink" and simultaneously killed the Mentor. (DW: Death to the Doctor!)