Rejected by the British Army in World War 1, because of a heart murmur.
Shares a birthday with his daughter Sara Karloff.
Suffered from chronic back trouble for most of his adult life, the result of the heavy brace he had to wear as part of his Frankenstein costume. He never let it slow him up, though, and kept active to the end of his life.
The mad scientist character in the Bugs Bunny short Water, Water Every Hare (1952) is patterned after Boris right down to his slight lisp and heavy eyebrows.
Took out his false teeth to achieve the metamorphosis in "Grip of the Strangler.".
Was one of the founding members of the Screen Actors Guild. His daughter recounts that, due to the Hollywood studio chiefs' distrust of unions and their attempts to keep them from forming, he always carried a roll of dimes in his pocket. This was because he had to use pay phones when conducting union business, since he knew his home phone had been tapped.
When he died, the New York Times obituary featured a picture of Frankenstein's monster. Unfortunately, the image was actually Glenn Strange in full makeup, not Karloff.
When he traveled to England to shoot The Ghoul (1933), it was the first time in nearly 25 years that he returned to his home country and reunited with the surviving members of his family,
When told by a mutual friend that Bobby Pickett, who recorded the hit song "Monster Mash", was a big fan of his, Karloff replied, "Tell him I enjoy his record very much." Pickett still considers that the greatest compliment he's ever gotten, and Karloff eventually sang the song himself on a television special.