Willis began by designing science fiction wargames for Metagaming Concepts, starting with Godsfire in 1976.
Willis's relationship with Chaosium proved the most enduring; he would turn to role-playing games.
With other members of Chaosium, he co-wrote the Ghostbusters RPG for West End Games, which won the H.G.
[1]: 91 After Greg Stafford left the company in 1998, Willis stayed on with Chaosium as its editor-in-chief.
[1]: 95 On September 11, 2008, the President of Chaosium, Charlie Krank, informed the public that Willis had been diagnosed with Parkinson's disease.