Comics are collected for several possible reasons, including appreciation, nostalgia, financial profit, and completion of the collection. The comic book came to light the pop culture arena in the 1940s due to the popularity of superhero characters Superman, Batman, and Captain Marvel. Since the 1960s, two publishers have dominated the comic book industry: Marvel Comics, publisher of such comics as Spider-Man, X-Men, and Fantastic Four, and DC Comics, which publishes titles such as Superman, Batman, and Wonder Woman. Other large non-manga publishers include Image Comics and Dark Horse Comics. As of 2006, numerous conventions and festivals are held around the world, with San Diego Comic Con being the largest and best-known convention in the United States.