Carl Sanford Joslyn "Sandy" Petersen (born September 16, 1955) is an American game designer. He is the principal designer of the Chaosium role-playing game Call of Cthulhu and drove its development for decades. After separating from Chaosium he continued to write and edit Mythos related game material such as the Malleus Monstrorum. He has now returned to Chaosium in the role of senior consultant and advisor with input into design, game balance and syncretising the disparate elements of different Mythos writers into the standardised and statistics based approach of the Chaosium games.
Prior to Call of Cthulhu Petersen worked long term on the rules for the RuneQuest games family as well as the Basic Role-Playing Game (BRG) universal rules, more recently released under an Open Games License (OGL).
Petersen also designed the lion's share of the levels for the video games DOOM and DOOM II.
Petersen was the Executive Producer for the 2011 movie The Whisperer in Darkness which received award nominations at the Chicago International Film Festival and Warsaw International Film Festival (Foreign Feature division). The film was produced by the H.P. Lovecraft Historical Society Motion Pictures team in the style of a 1930s black and white horror movie.
- Call of Cthulhu (1981)
- Shadows of Yog-Sothoth (1982)
- Cthulhu Companion (1983)
- Curse of the Chthonians (1984)
- S. Petersen's Field Guide to Cthulhu Monsters (1988)
- S. Petersen's Field Guide to Creatures of the Dreamlands (1989)
- Cthulhu Classics (1989)
- The Asylum & Other Tales (1990)
- Malleus Monstrorum