Boris Karloff was the pseudonym of William Henry Pratt, and English actor who, by fate and circumstance, ended up as one of Hollywood's Big Three horror film stars of the first two decades of the sound era, including Bela Lugosi and Lon Chaney, Jr.
His most famed role was as the square-headed monster of Dr. Frankenstein:
But, he essayed many other roles, until ending his career, like his peers, doing low budget horror films to pay the bills. His last great role was as the narrator in the cartoon version of Dr. Seuss's How the Grinch Stole Christmas.
He also did voiceover work for many other cartoons.
He did films with both Chaney and Lugosi, but got his best kudos for those with Lugosi. It was Lugosi, ironically, who helped launch Karloff's career, by refusing to play the Frankenstein monster.
