Mapother was born in Louisville, Kentucky, the son of Louisa (née Riehm) and william Reibert Mapother Sr. He is of English, Irish, and German ancestry. He is a first cousin of actor Tom Cruise (whose birth name was Thomas Cruise Mapother IV). His father was an attorney, bankruptcy consultant and judge in Louisville, between 1967 and 1970; william Sr., died on June 22, 2006, after fighting lung cancer and pulmonary fibrosis.