Much has been written about the presidency of the late George H. W. Bush. But in her new memoir, The Man I Knew, Jean Becker — Bush's chief of staff for a quarter-century — zooms in on the 25 years that came after his time in office. "One of the reasons why I wrote the book is I really felt the American people, when he left the White House, still didn't really understand who this man was," Becker, 65, tells PEOPLE. "He was a bigger-than-life person, smart, funny and had a heart as big as Texas. Until the day he...