In J.K. Rowling’s Harry Potter series, Hermione Granger’s cat is called Crookshanks.
Hermione buys the large, ginger cat at Magical Menagerie shortly before her third year at Hogwarts. Crookshanks becomes important in Harry Potter and the Prisoner of Azkaban, particularly during the conflict involving Ron Weasley’s rat, Scabbers.
Crookshanks appears to recognize that Scabbers is not an ordinary rat. He repeatedly pursues him, and the apparent hostility is eventually explained when Scabbers is revealed to be Peter Pettigrew, an Animagus hiding in animal form.
Crookshanks is distinct from several other animal companions in the series. Trevor is Neville Longbottom’s toad, Fang belongs to Hagrid, and Scabbers initially appears to be Ron’s pet rat. Those names are common mix-ups in character questions.