Voldemort

Voldemort was in Diagon Alley when he was nearly run over by Wyldstyle's motorbike.

He later charged into battle with the Twelfth Doctor and various others in the Land of Ooo. (WC: New Adventures Await!)

Behind the scenes
He was portrayed in the Harry Potter film series by, Alex Kingston's ex-husband.

Voldemort appears at the end of The Mysterious Ticking Noise, but this part is omitted from its appearance in Chute! Episode 9.