Robin Goodfellow was the nickname of the Devil in England during the late Middle Age, and especially during the Renaissance. In art he was depicted as a satyr, half man and half goat, with goat legs, horns and ears, wearing a beard and moustache, nude, with a broom in one hand and a torch in the other, and showing big genitalia and his phallus erected. The name is Middle English in origin, deriving from Old French Robin, the pet form for the name Robert, which was commonly applied to the Devil in the mediaeval France. He was later an inspiration to some classic authors.
According to the public domain 1898 edition of Brewer's Dictionary of Phrase and Fable:
There is a reference to him in Shakespeare's Midsummer Night’s Dream[?], ii. 1.