William Mapother is an American actor. His Hollywood career started in the late 1980s. His debut was in the film Born on the Fourth of July. In the ’90s, he appeared in the films Without Limits and Magnolia. He continued his film career the following decade. During this period, he had roles in the films Mission: Impossible 2, Suspect Zero, The Grudge, Lords of Dogtown, and The Zodiac, among others. He also portrayed Jason Thomas in the biographical film World Trade Center. Also in the 2000s, he became known for his role as Ethan Rom in Lost. In the 2010s, he played Richard Haibach in The Mentalist. He also appeared in the movies Underdogs, I Origins, The Atticus Institute, and Blackhat.