Mark Gatiss will appear in the fourth season of HBO's GAME OF THRONES. The British writer-producer-actor has written "Doctor Who" novels and episodes of the BBC cult classic, as well as acted on the long-running series (since 2007, he’s credited to three different roles on IMDB). In addition, Gatiss is the co-creator and co-star of another Brit-based favorite, SHERLOCK, where he plays Holmes’ dryly mysterious brother Mycroft. The GoT team is keeping Gatiss' role quiet.