Boris Karloff stars in the quintessential monster film, Frankenstein directed by James Whale (1931). Leaner and hungrier (literally) than he would appear in 1935's Bride of Frankenstein, Karloff became an icon with this film. 
A native of Hungary, Bela Lugosi (born Béla Ferenc Dezsõ Blaskó) was nearly 50 years old when he played the iconic count in Tod Browning's 1931 Dracula. Dracula at All Movie
Dracula at IMDb
Read Dracula by Bram Stoker (for free) thanks to Project Gutenberg
or, listen to the book (also thanks to Project Gutenberg)
Better known for his role as the creature in Frankenstein, Boris Karloff brings long "dead" Egyptian priest Imhotep to life with chilling results in 1932's The Mummy. A special nod to Karl Freund's direction, a great example of what one could do with a camera, even in the early '30s. 
The classic H.G. Wells novel became a vehicle for Claude Raines (directed by James Whale of Frankenstein fame). A tale of the corrupting influence of power, The Invisible Man utilized landmark special optical effects that influenced generations of filmmakers. 
Phantom of the Opera (1925) made Lon Chaney a star and Universal the go-to studio for horror films in the 1930s. Give me spirit gum and imagination over digital effects any day.
