Warren Girard Ellis is an English comic book writer, novelist, and screenwriter, born on 16 February 1968 in Rochford, Essex, England. He is best known as the co-creator of several original comics 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, he has written several Marvel series, including Astonishing X-Men, Thunderbolts, Moon Knight, and the "Extremis" story arc of Iron Man, which served as 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. He wrote the video games Hostile Waters (2001), Cold Winter (2005), and Dead Space (2008). He also wrote the animated TV movie G.I. Joe: Resolute (2009), the English version of Marvel Anime (2010–2011), and served as the head writer on the acclaimed animated Netflix series Castlevania (2017–2021).

Ellis is well known for his sociocultural commentary, both through his online presence and through his writing, which covers transhumanist and folkloric themes, often in combination with each other. He is a humanist and former patron of Humanists UK, a charity focused on promoting humanism and advancing secularism. He resides in Southend-on-Sea, England.