What was Vincent Price's first horror film?

Vincent Leonard Price Jr. (May 27, 1911 – October 25, 1993) was an American actor best known for his performances in horror films, although his career spanned other genres, including film noir, drama, mystery, thriller, and comedy. He appeared on stage, television, and radio, and in more than 100 films. He has two stars on the Hollywood Walk of Fame, one for motion pictures and one for television. He was born and raised near St. Louis, Missouri and has a star on the St. Louis Walk of Fame.

His first venture into the horror genre, for which he later became best known, was in the Boris Karloff film "Tower of London" (1939).

"Tower of London" is a 1939 black-and-white historical film and quasi-horror film released by Universal Pictures and directed by Rowland V. Lee. It stars Basil Rathbone as the future King Richard III of England, and Boris Karloff as his fictitious club-footed executioner Mord. Vincent Price, in only his third film, appears as George, Duke of Clarence.