Captain America is an American fictional character, a superhero who appears in comic books published by Marvel Comics. The character first appeared in Captain America Comics #1 (cover-dated March 1941), from Marvel Comics' 1940s predecessor, Timely Comics, and was created by Joe Simon and Jack Kirby. As of 2007, an estimated 210 million copies of "Captain America" comic books had been sold in 75 countries. For nearly all of the character's publication history, Captain America has been the alter ego of Steve Rogers, a frail young man who was enhanced to the peak of human perfection by an experimental serum, in order to aid the United States government's efforts to win World War II. Captain America wears a costume that bears an American flag motif, and is armed with an indestructible, boomerang-like shield that can both be thrown as a weapon and used to defend against others' weapons.