Modeled after Conrad Veidt's character in the 1928 film The Man Who Laughs (which was based on a novel by Victor Hugo), the Joker is a prank-obsessed criminal with a clown-like appearance, who likes to kill people with fatal hilarity. Writers have alternatively portrayed him as a goofy trickster-thief or as a homicidal psychopath with a warped sense of humor. Recent writers of the Batman comic book series have preferred the latter, and the Joker has been responsible for numerous tragedies in Batman's life, such as the murder of Jason Todd, the successor to the mantle of Robin after Dick Grayson, the injury/paralysis of Barbara Gordon, a.k.a. Batgirl/Oracle, and the death of Sarah Essen, Jim Gordon's wife.
The Joker is regarded by fans and comic-book afficionados as one of the greatest villains in comic-book history and by many the one with the most psychological depth. Created by Batman co-creator/writer Bill Finger and artist Jerry Robinson (while on staff under Batman co-creator/artist Bob Kane), the Joker first appeared in Batman #1 (1940).