Chicago native William O'Leary was born in 1957 to an FBI operative and began acting at age seven. He embarked on an acting career in the 1980s, appearing on stage in Seattle productions of Da, The Adventures of Huck Finn, and Cloud 9 before making his Broadway debut in Precious Sons in 1986 opposite Ed Harris. He moved on to film and TV work with credits in Nice Girls Don't Explode (his movie debut), Bull Durham, Candyman: Farewell to the Flesh, and Hot Shots! He's best remembered as Tim Allen's youngest brother, Marty Taylor, on Home Improvement. When the series concluded in 1999, O'Leary continued to act and landed parts in major films such as Terminator 3: Rise of the Machines and Miss Congeniality 2: Armed and Fabulous, as well as guest spots on various TV shows (NYPD Blue, CSI: Miami, Karen Sisco, 24). In 2009 he became the voice of the evil Gen. Xaviax on the animated series Kamen Rider: Dragon Knight. He owns and operates the Los Angeles acting school The Actors Path.