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Keith Martin
Carl Lynwood Sargent was a British parapsychologist and author of several roleplaying game-based products and novels, who used the pen name Keith Martin to write Fighting Fantasy gamebooks.
Excerpt from Wikipedia, available under CC BY-SA 4.0.
Books
Stealer of Souls
1988
ISBN 9780140326581
Steve Jackson and Ian Livingstone present Tower of Destruction
1991
ISBN 9780140344851