During this period, he also appeared in several films by Director Ernst Lubitsch, a fellow German émigré, including Ninotchka (1939) and To Be or Not to Be (1942). He played the role of Professor Herman Von Reiter in Shining Victory (1941), an adaptation of an A. J. Cronin play. Ruman continued his trend of playing over-the-top German characters later in his career for Lubitsch's protege Billy Wilder, appearing in Wilder's films The Emperor Waltz (1948), Stalag 17 (1953), and The Fortune Cookie (1966).