William J. Mann (born August 7, 1963) is an American novelist, biographer, and Hollywood historian best known for his studies of Hollywood and the American film industry, especially his 2006 biography of Katharine Hepburn, Kate: The Woman Who Was Hepburn. Kate was named one of the 100 Notable Books of 2006 by The New York Times. William J.Mann also used the pseudonym Geoffrey Huntington under which he wrote the Ravenscliff Series.