The most remarkable thing about Joshua Kendall’s new biography of cartoonist Garry Trudeau is that it exists at all. The Doonesbury creator is notoriously reclusive. He has been called “the J.D. Salinger of comics.” In 1975, Time magazine told the then-27-year-old Trudeau that they wanted to do a cover feature on him. He agreed to an interview but threw up the night before and called it off. He has kept his silence, with a handful of exceptions, ever since.