Captain Hammer is the main antagonist of Dr. Horrible's Sing-Along Blog.
Despite technically being a superhero, he is ironically more evil than his supervillain nemesis, Dr. Horrible (Real name: Billy). Captain Hammer just acts like a hero so he can have sex with women, and to spite Dr. Horrible. He enters the film by attempting to thwart one of Dr. Horrible's heists, inadvertantly meeting Penny, Dr. Horrible's crush. As the two fall in love, Dr. Horrible becomes enraged and plans to assassinate Hammer in order to join the Evil League of Evil. Meanwhile, Hammer is at a press conference, giving quite possibly the most insulting speech ever to the homeless. After Captain Hammer sings the song "Everyone's a Hero", Dr. Horrible appears and stops him with his Freeze Ray. However, Horrible cannot bring himself to kill Hammer, and the Freeze Ray shuts down. Hammer punches Horrible in the face, damaging the Death Ray in the process. Hammer is done in by his own arrogance when, refusing to listen to Horrible's warnings, attempts to fire the malfunctioning Death Ray, which explodes, causing Hammer to feel pain for the first time in his life. The blast also kills Penny, gaining Dr. Horrible infamy, as well as entry into the Evil League of Evil. During the final song "Everything You Ever", Captain Hammer, now reduced to a crying mess, is seen with a psychiatrist.
Captain Hammer is played by Nathan Fillion.