William T. Phillips

William T. Phillips (1863 – 1937) was a writer from Spokane, Washington, best remembered for The Bandit Invincible, a biography of the outlaw Butch Cassidy. A copy of the book is held at the American Heritage Center at the University of Wyoming. Phillips claimed to have known Cassidy since childhood, and stated in his book that Butch Cassidy's real name was not Robert Parker.

In his 1977 book In Search of Butch Cassidy, Larry Pointer speculated that Phillips was actually Cassidy, based upon stories in The Bandit Invincible and a resemblance between the two men.