Mager began his acting career in the 1990 biopic thriller Reversal of Fortune as Alexander Von Auersburg. The film co-starred J.D. Cullum and Tom Wright. In 1991 Mager appeared in another biopic, the Oliver Stone directed The Doors with Frank Military, Mark Moses and Titus Welliver. Also that year, Mager played Alexander Onassis in A Woman Named Jackie with Stephen Collins, Bob Gunton, Wendy Hughes, Nan Martin, Mark Metcalf, Tim Ransom and Nancy Youngblut. Mager then was in 1993's Blue Flame with Joel Brooks. Mager appeared in 1997's Big City Blues with Guy Siner. In 2000 Mager acted in The Beach Boys: An American Family opposite David Spielberg, Ned Vaughn and Clay Wilcox. In 2001 Mager worked on his first animated film, Cowboy Bebop with Nicholas Guest. Also that year was the western Woo