In an interview with Kobold Quarterly, Mutants & Masterminds designer Steve Kenson explains how he created the superhero game that’s one of the most successful non-fantasy games to be released using the D20 System:
Essentially, M&M started with Freedom City. I designed the core of the setting as a freelance project, but plans to publish it fell through, so the project reverted to me. I continued to work on it in my spare time, fleshing it out even further.
I happened to discuss the setting with Chris Pramas, saying it was a pity because, at the time, there were no superhero RPG publishers to whom I could pitch the setting. Chris asked to take a look at it and proposed the idea of a two-book deal: I would design a d20 superhero RPG for Green Ronin and they’d publish Freedom City as the companion setting book. So I designed Mutants & Masterminds and it was popular enough for Green Ronin to continue the line and later hire me on as developer full-time.
Kenson’s next project for the line is a sourcebook called The Supervillain’s Handbook, which he describes as “a big guide to villains and villainy for the game.” He says that it’s the largest book he’s worked on for Mutants & Masterminds since Ultimate Power.