The Catcher was a Spy: The Mysterious Life of Moe Berg by Nicholas Dawidoff

A major league catcher who went to law school in the off-season and spoke 5-7 languages joined the OSS and spied on German scientists and nuclear bomb experimenters in Italy and Switzerland. Very reclusive even after hundreds of interviews. The author paints a very shadowy picture of the spy who knew Babe Ruth, Joe DiMaggio, and Nelson Rockefeller.