Steffan O'Sullivan was a writer for GURPS products including GURPS Swashbucklers (1990) and GURPS Bunnies & Burrows (1992).^[1]: 319 He designed the FUDGE role-playing game system, first releasing it for free on the internet on December 7, 1993.^[1]: 319 His friend Ann Dupuis wanted to start her own game company, using FUDGE as its flagship game; O'Sullivan agreed, as long as she allowed the game to remain available for free on the internet, so Dupuis formed Wild Mule Games and published FUDGE in a limited print run in 1994.^[1]: 319 Dupuis changed the company's name to Grey Ghost Press in 1995, and convinced O'Sullivan to work up a new FUDGE ruleset, published on the internet in June 1995, and released later that year as the first large-scale FUDGE release from Grey Ghost Press.^[1]: 320 O'Sullivan changed the name from FUDGE to Fudge in 2000, and transferred the rights to the game to Grey Ghost Press officially in March 2004.^[1]: 320 O'Sullivan wrote the Princess Bride role-playing game using the FUDGE system, which was published by Toy Vault in 2019.^[2]

Among his works are the GURPS system books Bestiary, Bunnies & Burrows, Fantasy Bestiary and Swashbucklers. He is also the collaborative author of the Fudge open gaming system and the Sherpa game.

He currently^[when?] lives in New Hampshire.

• Steffan O'Sullivan's home page
• Steffan O'Sullivan on the Steve Jackson games page