Crookshanks
Crookshanks is the pet cat of Harry Potter character Hermione Granger. Crookshanks is obtained in the third book, Harry Potter and the Prisoner of Azkaban. Crookshanks is described as having ginger fur. Hermione bought Crookshanks from a shop in Diagon Alley out of sympathy, as nobody wanted him due to his face, which looked squashed. Crookshanks had a habit of trying to hunt down the pet rat of Ron Weasley, Scabbers. This caused a great deal of fighting between Ron and Hermione in the third book.
Spoiler warning: Plot or ending details follow.
Crookshanks is part Kneazle, giving higher than normal cat intelligence. Due to this, he noticed that Scabbers was really Peter Pettigrew, and that a large black dog living on the school grounds was really Sirius Black. Sirius eventually made Crookshanks trust him and sent him to help bring him Pettigrew, hence the reason he was always going after Scabbers.
When Ron first got Pigwidgeon, he used Crookshanks to test if it was really an owl.
There is some speculation that Crookshanks is a familiar.
