title: Batman (comic book)
context: Batman is an ongoing American comic book series featuring the DC Comics superhero Batman as its main protagonist. The character first appeared in Detective Comics #27 (cover dated May 1939). Batman proved to be so popular that a self-titled ongoing comic book series began publication with a cover date of Spring 1940.[2][3] It was first advertised in early April 1940, one month after the first appearance of his new sidekick, Robin, the Boy Wonder.
question: When was the first Batman comic published?
answers: May 1939