James Atlas asks in today's New York Times Book Review (My Subject, Myself) "How many American writers -- that is to say, novelists or poets -- have written biographies?" I immediately thought of one he had missed: novelist Evan Connell's richly contextualized, vivid and tragic biography of America's great genocidal maniac, George Armstrong Custer. See my note on Son of the Morning Star (1984).
Also, while you're in the NYTBR, don't miss A. O. Scott's essay, God Bless You, Mr. Vonnegut. Mr. Vonnegut, of course, is the very opposite of a genocidal maniac.