The Music Meister; sings the song that the world wants to hear,
Let’s not fight, let’s get along, for your hypnotic proprietor.
Batman: The Brave and the Bold, Season 1, episode 25: "Mayhem of the Music Meister"
One of the best musical episodes of any cartoon EVER! Starring Dr. Horrible himself: Neil Patrick Harris! It is basically a 22 minute villain song and it is GLORIOUS!
Go check it out on Netflix.