How many movies have Boris Karloff and Edward Van Sloan acted in together?

They have worked on 5 movies together! Their first movie together was Frankenstein (1931) and was their highest rated movie together. They have not worked together since Before I Hang (1940). They are most known for their horror films together.

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Dr. John Garth
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Dr. Ralph Howard
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Baron Gregor de Berghman / Anton de Berghman
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Doctor
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Imhotep, alias Ardath Bey
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Dr. Muller
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Jim Henderson
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Dr. August Steiner / Dr. Alec Munsell / Mr. X