There couldn't really be any other entry at number one. The ultimate crossover between Doctor Who and Sherlock, Mark Gatiss is the only person on this list to appear in and write for both shows. Being a lifelong fan of both Doctor Who and Sherlock Holmes, Mark Gatiss was the first writer to script an episode for the modern series of the sci-fi show after Russell T Davies and he later co-created Sherlock with Steven Moffat. In 2007, he came up against David Tennant's Doctor as Professor Lazarus, a mad scientist who wants to reverse the aging process but instead turns himself into a rampaging scorpion monster in The Lazarus Experiment. Under Moffat's tenure in Doctor Who, he has made two more, less noticeable, appearances in the show as spitfire pilot Danny Boy who fights the Daleks in his own episode Victory Of The Daleks and later as Gantok, a nasty alien who plays a deadly game of chess against the Doctor in Series Six finale The Wedding of River Song. All these roles dwarf in comparison, however, to Gatiss' turn as Mycroft, Sherlock's civil servant brother with whom he has an endless sibling rivalry. Perhaps Gatiss could one day appear as the Doctor's brother too? Enjoy this list? Or have we missed out an actor who you spotted in both Doctor Who and Sherlock? Let us know in the comments!
