The Jabberwock is a scary character from a poem in the book ‘Through the Looking-Glass and what Alice found there’ and is mentioned in the first chapter.
The poem in which he appears is called ‘Jabberwocky‘ and therefore the Jabberwock is often mistakenly referred to as ‘the Jabberwocky’.
The poem tells the story of a brave man who sets out to slay the Jabberwock, and finally returns home with his head.
The Jabberwock apparently lives on an island. In a letter to Mrs. Chataway, the mother of a child-friend, Carroll explains that the scene of the ‘Snark’ is “an island, frequented by the Jubjub and Bandersnatch – no doubt the very island where the Jabberwock was slain.”
(Source: Gardner, Martin. The Annotated Alice. The definitive edition, Penguin Books, 2001, p.161)
Tenniel’s illustration of the Jabberwock was originally intended as the book’s frontispiece, but it turned out to be so horrible that Carroll thought it might be better to replace it with another one.
The Jabberwock was no character in Disney’s cartoon movie. The Cheshire Cat does however sing the first verse of the poem.