The superhero Batman has appeared in many American comic books published by DC Comics since 1939, accumulating a number of recognizable supporting characters. The first Batman supporting character was Commissioner James Gordon, who first appeared in the same comic book as Batman in Detective Comics #27 (May 1939), and is Batman's ally in the Gotham City Police Department. Robin, Batman's sidekick, was introduced in the Spring of 1940, Alfred Pennyworth, Batman's butler, was introduced in 1943 and Barbara Gordon who was introduced in 1967. Batman also forms strong bonds or close working relationships with other superheroes, including Justice League members Superman, Green Arrow and Zatanna, as well as members of the Outsiders superhero team. Others such as Jason Bard, Harold, Onyx, and Toyman work for him.