Cyrus Xavier is the lead singer and leader of the Dudes of Darkness, a heavy metal garage band influenced by musical acts like KISS and Ozzy Osbourne and based out of A Nigma High. Sirus himself shares the same trademark top hat as famous guitarist Slash of Guns N' Roses.
Cyrus was present at the Prank, barfing into his top hat as a result of the stink bomb. Despite this, he took the liberty of complimenting Lee Ping on the choice of music used.
Cyrus pirated the music used during the Prank, getting a sponsor in the form of the Green Apple Splat soft drink company and having Lynch play the music at Brandy's party. It's explained that Cyrus developed a Gollum like obsession with the music as a result of it's hypnotic effects.
Meeting up with Lee who was hoping to examine the music for clues, the music contains background noise from the Prank. Cyrus wanted a clean version of the music in exchange. Unfortunately a sarcastic suggestion by Lee combined with the music's hypnotic effects prompts Cyrus to quit the Dudes of Darkness.
Lee is able to track down Cyrus and tries to use the music to get him to rejoin the band and give him the music. Lee soon discovers that Principal General Barrage's voice snaps Cyrus out of the trance. During the famous battle of the bands Lee is able to get Barrage to yell at Cyrus over the phone in time for him to rejoin the band and take them to victory, playing the band's number alongside Lee on the Violin.
As a thanks Cyrus gives Lee his copy of the music as he requested before deleting it from his own phone and offers Lee a place in the band to which he politely refuses. He does however give Lee one of his hats which Lee later gives to Biffy Goldstien.
Almost whenever he speaks he plays guitar and sings it. He also sometimes copies what people say by singing it.