Mark Gatiss (/ˈɡeɪtɪs/; born 17 October 1966) is an English actor, comedian, screenwriter, director, producer and novelist. He is best known for his work on television, acting in and co-creating shows with Steven Moffat. Gatiss has received several awards, including a BAFTA TV Award, a Primetime Emmy Award, a Peabody Award, and two Laurence Olivier Awards.

Gatiss co-created, co-wrote and acted in the BBC comedy series The League of Gentlemen (1999–2002). He co-created and portrayed Mycroft Holmes in the BBC series Sherlock (2010–2017) and Frank Renfield in the BBC / Netflix miniseries Dracula (2020). He also wrote several episodes of Doctor Who during Moffat's tenure as showrunner and two episodes during Russell T Davies' earlier tenure. His other TV roles include Tycho Nestoris in Game of Thrones (2014–2017), Stephen Gardiner in Wolf Hall (2015), and Peter Mandelson in Coalition (2015). He has acted in films such as Victor Frankenstein (2015), Denial (2016), Christopher Robin (2018), The Favourite (2018), The Father (2020), Operation Mincemeat (2021), and Mission: Impossible – Dead Reckoning Part One (2023).