KOTOBUKIYA offers products for well known comic book franchises, such as Batman and Superman. Comic books are often called comics for short. Although the term implies otherwise, the subject matter in comic books is not necessarily humorous, and in fact its dramatic seriousness varies widely. American comic books have become closely associated with the superhero sub-genre. Since the invention of the comic book format in the 1930s, the United States has been the leading producer with only the British comic (during the inter-war period and up until the 1970s) and Japanese manga as close competitors in terms of quantity.