Number 51 is an alien who was a former Stonecutter. His rank is more than likely a reference to "Area 51".
History[]
He sings "The Stonecutters Song" along with the other Stonecutters. It is unknown whether he joins The Ancient Mystic Society of No Homers.
Non-canon[]
Treehouse of Horror X[]
He is seen in the audience while Kang and Kodos are on stage.
Appearances[]
Episode – "Homer the Great"
Episode – "All Singing, All Dancing" (archive footage)
THOH – "Treehouse of Horror X"
Episode – "The Flandshees of Innersimpson" (archived; remix during closing credits)
Video game – The Simpsons: Tapped Out