Paul Cain was the pen name used by George Carol Sims (born May 30, 1902 in Des Moines, Iowa, died June 23, 1966 in North Hollywood, California), an American pulp fiction author and screenwriter. He was the author of 17 short stories in Black Mask and one book, Fast One. Fast One is considered to be a landmark of the pulp fiction genre and was called the "high point in the ultra hard-boiled manner" by Raymond Chandler.
Writing under the pen name Peter Ruric, Sims enjoyed a brief career in Hollywood as a screenwriter during the 1930s, including writing the screenplay for the Boris Karloff vehicle The Black Cat. He died in North Hollywood in 1966.