Oscar has a green body, and lives in a trash can. His favorite thing in life is trash; evidence for this include the fact that he has never been shown outside his trash can on a single episode, and the song "I Love Trash". He's known as "The Grouch" because of his typically grouchy moods, which tend to be on the whiney side, although he can also be very clever. Also, he is of the grouch species. Some say he is very smart.
See also: List of Sesame Street Grouch characters