Mark Millar is a Scottish comic book writer who first gained fame with his run on the superhero series The Authority, published by DC Comics' Wildstorm imprint. He has written extensively for Marvel Comics, including notable runs on The Ultimates, described as "the comic book of the decade" by Time magazine and a significant inspiration for the 2012 film The Avengers. Millar's work includes X-Men, Fantastic Four, and Avengers for Marvel's Ultimate imprint, as well as Marvel Knights Spider-Man and Wolverine.

In 2006, Millar wrote the Civil War mini-series, the centerpiece of a company-wide crossover storyline and the inspiration for the film Captain America: Civil War. The "Old Man Logan" storyline from his Wolverine run inspired the 2017 film Logan.

Millar has created numerous series under the Millarworld label, including Wanted with J. G. Jones, Hit-Girl & Kick-Ass with John Romita, Jr., and Nemesis with Steve McNiven, among others. Many of these series have been adapted into films and series, such as Wanted, Kick-Ass, Kingsman: The Secret Service, and Jupiter's Legacy.

Beyond writing, Millar is an executive producer for all film and television adaptations of his comics. From 2012 to 2016, he served as a creative consultant for 20th Century Fox on adaptations of Kick-Ass and The Secret Service.

In 2013, he was appointed a Member of the Most Excellent Order of the British Empire (MBE) for services to film and literature.