Agnes Nitt (not to be confused with Agnes Nutter
from "Good Omens") is one of the witches of Lancre
in Terry Pratchett
books. She's one of those insecure fat girls
whom everyone patronizingly compliments on having great hair and a wonderful personality. Much of her magical talent is tied up in her voice. Agnes has an outstanding voice
, capable of doing uncanny imitations and even singing an aria
in tune with herself.
She first appeared as a background character in Lords and Ladies, as a wanabee witch whom Granny Weatherwax and Nanny Ogg noticed did have some genuine magical talent. Agnes became a major character in Maskerade, where she left her homeland to become a star at the Ankh-Morpork opera house. While Agnes had her incredible voice, her less-than-stellar looks meant she got pushed into the chorus, while her "friend" Christine, a frail-spirited, vapid, pretty young thing who suffered from gratuitous exclamation marks, got the leading roles, and Agnes had to make up for Christine's lack of singing ability. Eventually, though, Nanny and Granny came looking for a third member for their coven (since Magrat had left to become full time Queen of Lancre), and after coming to her senses and helping them outwit a murdering phantom, Agnes agreed to go back to Lancre.
They say that inside every fat person is a thin one trying to get out (and a lot of chocolate, but that's beside the point), and Pterry made this manifest in Agnes's alternate personality, Perdita X. Dream. Perdita is cynical, cool-headed, bold, anti-authority, and a lot of other things Agnes isn't in normal circumstances. If Perdita were made manifest, she would undoubtedly be some skinny goth chick who wears black all the time and sniggers at authority behind its back.