Greebo

Greebo is a character in Terry Pratchett's Discworld books. He is a foul-tempered tomcat whose owner, Nanny Ogg, insists against all the evidence that he is a sweet, harmless kitten. In the course of the books, he has killed a vampire, eaten a vampire, and been transformed into a shy young man by Nanny Ogg.

A Greebo is also a young person who wears a leather jacket and rides a motorbike; an abbreviation of Grease Boy.