He was the toast of Cambridge, a shining example of erudite, literary culture. There was just one problem. He was an alumnus to make Harvard proud. The son of a renowned Munich art dealer and a blueblooded Boston mother, Ernst Franz Sedgwick Hanfstaengl, who graduated in 1909 with a degree in history, spoke four languages and moved easily in international circles. As a student he had thrown himself into campus life, rowing with the varsity crew, cheerleading at football games, and performing at the Hasty Pudding Club -- where he was in demand, The Boston Globe noted, "for theatricals, musical...