Who is Puck, or Robin Goodfellow, from A Midsummer Night's Dream from The Sandman and what is their importance?

Puck is a hobgoblin who is a servant of Auberon. Puck is reputed to be vicious and even psychotic. He is taken with Shakespeare's play, and he decides to murder the actor playing him and take on the role of impersonating himself. When the rest of the fairies leave for the fairy realm, Puck stays behind in the human world. No one knows what ultimately becomes of Puck.