Question: Who designed The City of Greyhawk and goes by the pen name Keith Martin?
Sentence (from "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.
Relevant evidence: Yes