King was born on May 28, 1949, in Storm Lake, Iowa, the son of Mildred Lila (née Culler), a homemaker, and Emmett A. King, a state police dispatcher. His father has Irish and German ancestry, and his mother has Welsh roots, as well as American ancestry going back to the colonial era. King graduated in 1967 from Denison Community High School. He is married to Marilyn, with whom he has three children. Raised a Methodist, King attended his wife's Catholic church, converting 17 years after marrying her. His son Jeff King (consultant) has been active in his political campaigns.