This Who's Who was originally featured in Issue 115 - November 2006 and was written by William Barnett
Greebo has been in the Discworld books as long as his mistress, Nanny Ogg. The fact that Nanny owns a cat whereas Granny Weatherwax is identified as 'an inveterate cat-hater' gives the reader a handy clue as to the differences in the two witches' personalities: Nanny has a human warmth that Granny Weatherwax seldom displays.
As a human, he's just as much of a menacing predator as when he's a cat.
It's a bit surprising that Granny Weatherwax is a cat-hater, though. Like most intelligent human beings (e.g., me), Terry seems to be a cat lover and he passes on this attribute to some of our favourite characters - Death springs to mind. 'Cat-hater', on the Discworld and in real life, is usually a pretty reliable shorthand for 'crap human being' but perhaps in Granny's case it's just part of her steely public persona.
Greebo returns in Witches Abroad when (probably with an eye on cat lovers among the readership) Nanny decides to take him with her on the witches' trip to Genua. Her justification for this is that 'He'll miss his mummy if he's left behind, won't he'. It turns out to be a providential decision.
In Genua, the witches manage to transform Greebo into human form. As a human, he's just as much of a menacing predator as when he's a cat. The witches initially complete the transformation without taking into account any clothes, leading Nanny Ogg to remark 'No wonder all the lady cats scream at night.' Greebo helps the witches out and subsequently makes his way to the kitchens, still human-shaped, for a plate of fish heads and a saucer of milk.
Greebo does more travelling, this time to Ankh-Morpork, in Maskerade. This is unlucky for the other people taking the Ankh-Morpork coach that day: Greebo makes a point of jumping on to their laps and making himself comfortable. 'And then, when he was sure they were resigned to the situation, he'd started to smell.' Most of the passengers quit the carriage and ride on top with the coachman instead. Greebo returns to human form a couple of times as well, notably as Granny's escort, Lord Gribeau.
What's great about Greebo is that he captures so much of what we see in our own cats. He's amoral, self-interested, he only loves Nanny because she feeds him, he jeers at his enemies when he thinks he's safe from them (I remember my old cat sitting on one side of a glass door washing himself while a neighbour's dog barked fruitlessly on the other side) and so on. For the non-cat lovers he might not be a particularly interesting character, but to those of us who dote on the selfish beasts ... well, Greebo is clearly the creation of a writer who knows his cats.
Favourite quote: "...pull up a chair and call the cat a bastard." (Nanny Ogg, "Wyrd Sisters")