The title of this article is a conjectural. Though the topic is found within The Simpsons universe, a proper name is not available.
The green alien is a former Stonecutter. In The Simpsons: Tapped Out, he is known by his Stonecutter rank, Number 51. This is more than likely a reference to "Area 51".
He sings "The Stonecutters Song" along with the other Stonecutters. It is unknown whether he joins The Ancient Mystic Society of No Homers.
Treehouse of Horror XEdit
He is seen in the audience while Kang and Kodos are on stage.