Greebo is a character in Terry Pratchett's Discworld books. He is first introduced in Wyrd Sisters. He is a foul-tempered one-eyed grey tomcat whose human, Nanny Ogg, insists against all the evidence that he is a sweet, harmless kitten. In the course of the books, he has killed two vampires, eating at least one of them in the novel Witches Abroad: The bat squirmed under his claw. It seemed to Greebo's small cat brain that it was trying to change its shape, and he wasn't having any of that from a mouse with wings on. To date, Greebo is known to fear only three things: