Joseph Hill "Joss" Whedon is an American screenwriter, executive producer, director, comic book writer, occasional composer and actor, founder of Mutant Enemy Productions and co-creator of Bellwether Pictures. He is best known as the creator and showrunner of the television series Buffy the Vampire Slayer , Angel , Firefly and Dollhouse , as well as the short film Dr. Horrible's Sing-Along Blog . Whedon wrote and directed the movie adaptation of Marvel's The Avengers which will be released in May 2012. He is also notable for his work in film, comic books, and online media. Many of Whedon's projects, as well as Whedon himself, enjoy cult status.