Passage: Nolan's inspiration for the film was the Joker's comic book debut in 1940, the 1988 graphic novel The Killing Joke, and the 1996 series The Long Halloween, which retold Two-Face's origin. The "Dark Knight" nickname was first applied to Batman in Batman #1 (1940), in a story written by Bill Finger. The Dark Knight was filmed primarily in Chicago, as well as in several other locations in the United States, the United Kingdom, and Hong Kong. Nolan used IMAX 70 mm film cameras to film some sequences, including the Joker's first appearance in the film. Warner Bros. initially created a viral marketing campaign for The Dark Knight, developing promotional websites and trailers highlighting screenshots of Ledger as the Joker. Ledger died on January 22, 2008, some months after the completed filming and six months before the film's release from a toxic combination of prescription drugs, leading to intense attention from the press and movie-going public.

Question: In the batman universe the Joker character was first introduced in what year?
1940