Hagen was born in Chicago, Illinois, to professional ballroom Dancers, Haakon Olaf Hagen and the former Marvel Lucile Wadsworth. When Haakon Hagen deserted his family, young Hagen was reared by his mother, grandmother, and aunts. As a 15-year-old, he relocated to Portland, Oregon, where one of his aunts had taken a teaching job. He attended Portland's Jefferson High School. His family returned to Chicago, and he attended Oregon State University in Corvallis and later the University of Southern California in Los Angeles, California, from which he received a degree in international relations. He spent a year in law school at the University of California, Los Angeles, and was subsequently employed by the U.S. State Department in West Germany, followed by a two-year stint in the United States Navy. For a time, he taught ballroom dancing, the specialty of his parents, for the Arthur Murray Company. Then, at the age of 27, he tried acting. He was spotted in a production of Eugene O'Neill's Desire Under the Elms and given a guest-starring role on the classic 1950s police series Dragnet, starring Jack Webb.