(Concise introduction for lay reader)* Marcus du Sautoy, "Finding Moonshine", Fourth Estate, 2008, ISBN 978-0-00-721461-7 (another introduction for the lay reader)* Ron Solomon (1995) "On Finite Simple Groups and their Classification," "Notices of the American Mathematical Society".
(Concise introduction for lay reader)*Marcus du Sautoy, "Finding Moonshine", Fourth Estate, 2008, ISBN 978-0-00-721461-7 (another introduction for the lay reader)* Ron Solomon (1995) "On Finite Simple Groups and their Classification," "Notices of the American Mathematical Society".