"Muggle-Wump" is a fictional character in some of Roald Dahl's books for children, and "the Muggle-Wumps" are his family. A Muggle-Wump appears in The Enormous Crocodile and there is a Muggle-Wump with a family in The Twits. A character resembling him (shown in Quentin Blake's illustrations) also appears in The Giraffe and the Pelly and Me. The first two stories have him almost as a symbol of retribution to the antagonists of the overall tale, whereas in the last one he is happy and safe.
The Enormous Crocodile
The Muggle-Wump of The Enormous Crocodile, after reasoning with the wily reptile that it is wrong to eat little children, loses his temper and, very nearly, his life, when the Crocodile bites into his tree to catch him. He gets revenge, however, by following the Enormous Crocodile and thwarting his chances at catching a child when they are about to come near him. In doing this he angers the Enormous Crocodile into wanting to eat more children, only to be thwarted by the Roly-Poly Bird (another recurring character in Dahl's books) and Trunky the Elephant who hurled the Enormous Crocodile into the sun.
The Muggle-Wump in this story has a wife and children and is subject to animal cruelty at the hands of Mr and Mrs Twit, who are retired circus trainers. They force the Muggle-Wumps to balance on their heads, one on top of the other, or else stand and walk on their hands- all at the peril of feeling Mrs Twit's "beastly [walking-]stick" across their bodies. Occasionally, it is said, one of Muggle-Wump's children will faint of the rush of blood to their heads. To add insult to injury, they are kept (when not subject to command) in a cage overlooking the Twits' garden, at the centre of which is a large dead tree that Mr Twit smears with glue to trap birds for his favourite dish of Bird Pie. When the monkeys shout warnings, the birds cannot understand their language and so are always caught.
Assisted by the Roly-Poly Bird, who arrives while on holiday in England, and who can speak both the African language of the monkeys and the English of the native birds, the Muggle-Wumps rescue the latter and escape from their cage while the Twits are away. Thereafter they attach all the Twits' living-room furniture to the ceiling with the glue used to trap the birds. They then, on the Twits' return, have two birds drop some glue on the couple's heads. On entering their house, the Twits believe that their living room has turned upside down and that they must therefore be standing on the ceiling, and so stand on their heads and become stuck. Muggle-Wump and his family are then able to return to Africa with the help of the Roly-Poly Bird, presumably to live happily ever after.
The Giraffe and the Pelly and Me
Possibly not a Muggle-Wump at all, but said to resemble them, this monkey refers to himself in the title "The Giraffe and the Pelly and Me". He is a window-washer by trade, and has a very good working relationship with his partners, the Giraffe whose neck can stretch out to any length and the Pelican ("Pelly), the top half of whose bill can collapse inwards like a tape-measure: the Giraffe is the ladder, the pelican (with his deeply pouched bill) is the bucket for the water, and the monkey cleans the windows with a cloth. He is an adept singer and dancer.
Whilst he is working for the Duke of Hampshire, the Monkey and the Giraffe notice an armed burglar stealing the Duchess' jewellery, whereupon the Pelican traps the thief in the pouch of his enormous bill and later gives him to the police. The Duke then allows the monkey and his friends to live on the grounds of his wealthy estate, and their house is reverted into its former function- a sweetshop- much to the delight of the narrator. The monkey then closes the story with a song.