Felix made three more movies, Weiße Majestät, Peer Gynt and Das Erbe von Pretoria (all 1934) in Germany before the Nazis expelled him.
In Hollywood, as was the fate for so many German actors and actresses of that time, like Conrad Veidt, he was mainly cast in Nazi roles, which kept him working during the war years.
Right after that movie, he received another small role as a German policeman in Desperate Journey starring Ronald Reagan, Errol Flynn and Raymond Massey.
Within weeks, at age 56, Ryen obtained the role which resulted in his best remembered performance, that of Colonel Heinze in Casablanca (1942), where he constantly had to tail his superior Major Heinrich Strasser (Conrad Veidt).
He had small roles in three movies in 1945, This Love of Ours starring Claude Rains, Salome Where She Danced with Yvonne De Carlo and Paris Underground.