Warren Girard Ellis (born 16 February 1968) is an English comic book writer, novelist, and screenwriter. He is best known as the co-creator of several original comic series, including Transmetropolitan (1997–2002), Global Frequency (2002–2004), and Red (2003–2004), which was adapted into the feature films Red (2010) and Red 2 (2013).

Ellis is the author of the novels Crooked Little Vein (2007) and Gun Machine (2013) and the novella Normal (2016). A prolific comic book writer, Ellis has written several Marvel series, including Astonishing X-Men, Thunderbolts, Moon Knight, and the "Extremis" story arc of Iron Man, which was the basis for the Marvel Cinematic Universe film Iron Man 3 (2013). Ellis created The Authority and Planetary for WildStorm and wrote a run of Hellblazer for Vertigo and James Bond for Dynamite Entertainment.