Boris Karloff (William Henry Pratt) (1887-1969) donned the monster's flattop and heavy asphalt-spreader's boots for Universal's 'Frankenstein' (1931), 'Bride of Frankenstein' (1935), and 'Son of Frankenstein' (1939).

When Karloff grew tired of playing the monster, Lon Chaney, Jr. (Creighton T. Chaney) (1906-1973) stepped into the role in 'The Ghost of Frankenstein' (1942).

Bela Lugosi (1882-1956), a star since his stage and screen portrayal of 'Dracula' (1931) agreed to play the monster in 'Frankenstein Meets the Wolfman' (1942), since Chaney would be playing the Wolfman and had already become famous in that role.

Glenn Strange (1899-1973) also played the monster for three more Universal movies before becoming more famous playing Sam Noonan, the bartender of the Longbranch Saloon on TV's 'Gunsmoke'.

John Carradine (1906-1988) did play Dracula, but never the Frankenstein monster.

More Info: en.wikipedia.org