Black Friday is a 1940 American science fiction horror film starring Boris Karloff and Bela Lugosi.

[6] Bookish college professor George Kingsley is accidentally run down by gangster Red Cannon, who was fleeing from four members of his former gang attempting to kill him.

Sovac is intrigued, not only because this suggests his procedure can be used to preserve a person's life indefinitely, but because Cannon has hidden $500,000 somewhere in New York City.

Cannon exploits the natural disguise of Kingsley's body to begin hunting down his former gang members and strangling them to death.

Police are baffled as to the identity of the "gangster killer", while his gang members assume he is an associate to whom Cannon passed on his knowledge before he died.

Before stepping into the electric chair he gives notes on his brain transplant procedure to a reporter, in the hopes that his work may one day be put to better use.

[7] In January 1939, Universal announced that Willis Cooper was working on the script, with Bela Lugosi and Boris Karloff probably to star.

Rather than a straight switch though, Lugosi was given the minor role of another gangster, while character actor Stanley Ridges was brought in to play the professor.

[10] In later years, writer Curt Siodmak claimed Karloff felt he was not a good enough actor to play the dual role of the kindly professor-turned-murderous gangster, but it is more likely that his appearance and voice could not be changed completely enough to make the switch convincing.

"[14] Diabolique magazine in 2019 described it as "Lubin's first film to have any kind of lasting legacy... because it features both Boris Karloff and Bela Lugosi, though neither share a scene together.