Who designed The City of Greyhawk and goes by the pen name Keith Martin?
The City of Greyhawk: The City of Greyhawk is a boxed set accessory for the World of Greyhawk campaign setting, part of the "Advanced Dungeons & Dragons" fantasy role-playing game. The City of Greyhawk:  It was designed by Doug Niles, Carl Sargent, and Rik Rose, and published by TSR in 1989. Carl Sargent: Carl L. Sargent (born December 11, 1952, in Caerleon, Monmouthshire, Wales) is a British parapsychologist and author of several roleplaying game-based products and novels, using the pen name Keith Martin to write Fighting Fantasy gamebooks.
Carl Sargent