Dr. Horrible (Real name: Billy) is the villain protagonist of Dr. Horrible's Sing-Along Blog.
Although he is technically a supervillain, Dr. Horrible has better intentions than Captain Hammer, his ironically more villainous superhero nemesis. His goals are to A) Win the heart of his crush, Penny, and B) Become part of the Evil League of Evil. His friend is his own sidekick Moist. As he boasts about his exploits via his vlog, he receives a letter from the League's leader, Bad Horse, stating (in song) that in order to be admitted, Dr. Horrible must commit a show of force ("A murder would be nice, of course"). Of course, he fails, and receives a phone call from Bad Horse saying that the only way to be accepted now is to commit an assassination. Horrible is initially hesitant, but after his nemesis Captain Hammer says that he's going to sleep with Penny merely out of spite, Horrible targets Captain Hammer and creates a Death Ray. After interrupting a press conference where Captain Hammer is speaking, he uses a freeze ray on his nemesis but can't bring himself to pull the trigger. Eventually the freeze ray shuts down, and Hammer strikes back, causing the Death Ray to malfunction and explode, causing Captain Hammer to feel pain for the first time, as well as killing Penny. Realizing that he technically assassinated Penny, he declares Pyrrhic victory. Although he succeeded in becoming part of the Evil League of Evil, he was also responsible for the death of the girl of his dreams. Therefore, he got everything he wanted but lost the one thing he wanted the most. Having lost the girl of his dreams to himself took away all of his good intentions.
Dr. Horrible was played by Neil Patrick Harris.