He started his career as a sub-editor for D. C. Thomson & Co. Ltd, where he met Wagner. In 1971 both left to go freelance, and were soon writing scripts for IPC's girls' and humour comics. After D.C. Thomson launched Warlord, a successful war-themed weekly, Mills was asked in 1975 to develop a rival title for IPC. Based in the girls' comics department to avoid the attention of the staff of the boys' department, Mills, along with Wagner and Gerry Finley-Day, worked in secret to create Battle Picture Weekly. Battle's stories were more violent and its characters more working class than IPC's traditional fare, and it was an immediate hit. Having made the comic ready for launch, Mills resigned as editor. He would later write the celebrated First World War series Charley's War, drawn by Joe Colquhoun, for the title.
After launching Battle, Mills began developing a new boys' title, Action, launched in 1976. Action's mix of violence and anti-authoritarianism proved controversial and the title lasted less than two years before being withdrawn in the face of media protests. It was briefly revived in neutered form before being merged into Battle.
His next creation was the science fiction-themed weekly 2000 AD, launched in 1977. As with Battle and Action he developed most of the early series before handing them over to other writers. He took over the development of Judge Dredd when creator John Wagner temporarily walked out, and wrote many of the early stories, establishing the character and his world, before Wagner returned.
In 1978 IPC launched Starlord, a short-lived companion title for 2000 AD. Mills contributed Ro-Busters, a series about a robot disaster squad, which moved to 2000 AD when Starlord was cancelled. Ro-Busters was the beginning of a mini-universe of interrelated stories Mills was to create for 2000 AD, including ABC Warriors and Nemesis the Warlock. Artist Kevin O'Neill was involved in the creation of all three. Nemesis in particular, featuring a morally ambiguous alien hero fighting a despotic human empire, allowed Mills to work out his feelings towards religion and imperialism. Another strand of his 2000 AD work was Sláine, a barbarian fantasy based on Celtic mythology and neo-paganism, which he co-created with his then wife Angela Kincaid (with whom he also created the children's series of books, The Butterfly Children).
He also had a hand in IPC's line of Horror comics aimed at girls such as Chiller.
He has had little success in American comics, with the exception of Marshal Law, a savage superhero satire published by Marvel Comics' Epic imprint in the late 1980s, drawn by O'Neill.
In 1986 he edited the short-lived comic Dice Man, which featured characters from 2000 AD. He wrote nearly every story.
In 1988 he was involved in the launch of Crisis, a politically aware 2000 AD spin-off aimed at older readers. For it he wrote Third World War, drawn initially by Carlos Ezquerra, a polemical critique of global capitalism and the ways it exploits the developing world. The title lasted until 1991 and launched the careers of talents such as Garth Ennis, John Smith and Sean Phillips.
In 1991 Mills launched Toxic!, an independent colour newsstand weekly comic with a violent, anarchic tone, perhaps as a reaction against the politically worthy Crisis, and a creator-owned ideal. Many of the stories were created by Mills and co-writer Tony Skinner, including Accident Man, an assassin who makes his hits look like accidents. Toxic! lasted less than a year, but gave a start to talents such as Duke Mighten and Martin Emond.
In 1995, he broke in the French market, one of his life's goals, with Sha, created with French artist Olivier Ledroit.
He continues to write Sláine, Bill Savage, Black Siddha and ABC Warriors for 2000 AD, and also the Franco-Belgian comic Requiem Vampire Knight, with art by Olivier Ledroit and its spin-off Claudia Chevalier Vampire, with art by Franck Tacito.
Two new series, Greysuit, a super-powered government agent drawn by John Higgins, and Defoe, a 17th century zombie hunter drawn by Leigh Gallagher, began in 2000 AD prog 1540. 2000AD Online - news zone
Mills has formed Repeat Offenders with artist Clint Langley and Jeremy Davis "to develop graphic novel concepts with big-screen potential" and the first project will be an, as yet unpublished, graphic novel called American Reaper. It has been optioned by Trudie Styler's Xingu Films and Mills has written the screenplay.
He has also written two Doctor Who audio plays, "Dead London" (2008) and "The Scapegoat" (2009) for Big Finish Productions, featuring the Eighth Doctor and Lucie Miller. The first audio play was released as the first part of the second season of the Eighth Doctor Adventures and the second as part of the third season.
