Black Friday (1940 film)

Black Friday is a 1940 American science fiction film starring Boris Karloff. Bla Lugosi, although secondbilled, has only a small part in the film and does not appear with Karloff. Writer Curt Siodmak would revisit this theme again in Donovans Brain 1953 and Hausers Memory 1970.

The original script cast Lugosi as the doctor and Karloff as the professor. For unknown reasons, Karloff insisted on playing the doctor. Rather than a straight switch though, Lugosi was given the minor role of a rival gangster, while character actor Stanley Ridges was brought in to play the professor.

Source: Wikipedia