William J. Mann is an American novelist, biographer, and Hollywood historian best known for his biography of Katharine Hepburn, Kate: The Woman Who Was Hepburn (2006). Kate was declared the "definitive" work about Hepburn by The Sunday Times and was named one of the 100 Notable Books of 2006 by The New York Times.

Mann was born in Connecticut and, after working briefly as a Capitol Hill aide, received his Master's degree at Wesleyan University. He worked as a journalist at Metroline magazine from 1992 to 1995. Mann published his first novel, The Men From the Boys, in 1997, and continued with a series of books featuring the same characters, including 2003's Where the Boys Are and 2007's Men Who Love Men. In addition, Mann has written the widely praised Wisecracker, a biography of film star William Haines, for which he won the Lambda Literary Award; Edge of Midnight: The Life of John Schlesinger; and Behind the Scenes: How Gays and Lesbians Shaped Hollywood.

In November 2006, Publisher's Marketplace reported that Mann's next biography, How to Be a Movie Star: Elizabeth Taylor in Hollywood, would be published by Henry Holt and Company on September 1, 2009.

Mann lives in Palm Springs, California, and Cape Cod, Massachusetts, with his partner, Dr. Timothy Huber.

Mann continues to chart the lives, lusts and losses of Jeff O'Brien and Lloyd Griffith, who first appeared in his 1997 novel, The Men from the Boys. This lively sequel finds them estranged after six years together, yet considering a reconciliation. The death from AIDS of their mutual best friend and mentor David Javitz sent them scurrying in different directions: Jeff to discover a blissful bachelorhood of drugs, circuit parties and dance floor groping in Boston, and Lloyd to adopt a peaceful, celibate Provincetown lifestyle, exploring his spiritual side and running a guesthouse with friend Eva. Can these two men find common ground again? Lurking in the background are several friends who stand in their way: Jeff's current squeeze, the independently wealthy Anthony; Henry, Jeff's smitten best friend; and the widowed, emotionally unstable Eva. Each reveals his or her own secrets while selfishly pecking away at Jeff and Lloyd's happiness. This is especially true of Henry, who is indebted to Jeff for helping to transform him from nerdy nobody to muscular hottie. The chatty story is related from different characters' perspectives, the better to reveal their occasionally earnest but generally shallow motives. Mann doesn't skimp on cattiness, camp and clever barbs, yet he addresses serious subjects-safe sex, gay families, moral responsibility-as well. But at more than 400 tight-packed pages, the onslaught of rapid-fire, sitcom-style repartee and melodrama may have some circuit boys leaving this dance early.