In the book, Tab is a male cat (but portrayed as female in the movie) who taunts his prey. He also has a sort of ambition to kill Hazel. When Hazel and Pipkin were trying to steal some hutch rabbits - Clover, Boxwood, Haystack, and Laurel - from the farm, Tab tried to creep up on them. Pipkin spotted him, however, and Hazel taunted the cat into jumping at them before they made their escape.
In the book there is also a female tortoiseshell cat from Nuthanger Farm whose name is unknown. This unnamed cat got into a fight with Bigwig and lost, with minor injuries. This cat is often mistaken for Tab.
In the animated series, Tab is characterized as a female cat, known as Tabitha.