Geoffrey Swivel was introduced in The Shepherd's Crown-the final Discworld book.
Geoffrey, the third son of Lord Swivel, is well educated, a vegetarian and a pacifist. This does not sit well with his father, especially since he is a spare wheel in the family, the father has a son and heir and a spare in case something happens to the heir. He doesn't need a third son who spends his time immersed in books instead of blood sports and takes no interest in Geoffrey, especially when Geoffrey displays his contempt for his father's hunting practices which he considers barbaric. After a confrontation with his father, Geoffrey hooks his goat, Mephistopheles, to his cart and heads towards Lancre, intending to become a witch.
Upon arrival, he meets Tiffany Aching, who decides to employ Geoffrey as a 'backhouse boy' or general dogs' body to help her out and starts teaching him the basics of caring for the people in the area - the first step to becoming a witch. He and his goat get on well with everybody, and Tiffany dubs him a calm-weaver after he defuses a number of potential problems. He befriends some of the old retired men who have time on their hands and are bored stiff. Intending to help the old men have some autonomy from their wives, he introduces the idea of sheds (Discworld's 'man caves').
After the Witches won the battle against the elves, Tiffany decides that she can't look after two steadings at once. Geoffrey replaces her in Lancre and takes on Esmerelda Weatherwax's old cottage and broomstick which is famous for being the only stick on the Disc to need jump-starting.