6. Adolf Hitler In "Let's Kill Hitler"
Hitler may not strictly qualify as a recurring Doctor Who character, but if he wasn't a formidable villain, I don't know who else would qualify. Anyway, Hitler's appearance in this episode is mostly restricted to the stuff of Benny Hill sketches as he spends his time locked up and fuming in a cupboard, completely reducing one of the most inhuman and evil figures in Earth's history to a throwaway gag and background scenery. This is inkeeping with the time-honored tradition of ridiculing tyrants as seen in media such as the Daffy Duck WWII cartoon which culminates in Daffy braining Hitler with a mallet, and the entirety of the post 9-11 South Park episode "Osama Bin Laden Has Farty Pants." (I laughed out loud just typing that.) Unlike those appearances though, Hitler takes a backseat to this plot-heavy outing that gives us River's origin story, several regenerations and some great acting by Matt Smith as he bravely fights against the effects of River poisoning him with the Janus Thorn. The best part of this episode, however, is the fact that no one bothers to ever let Hitler out of that cupboard. Is he still in there?