Mrs Norris is a cat own by Argus Filch, the caretaker at Hogwarts School of Witchcraft and Wizardry. She patrols the school and should any student break a rule infront of her, she will whisk away to find Filch and bring him to the scene of the crime. Flich is very fond of his cat.
 First Book
 Second Book
In 1992 the school was shocked when Mrs Norris was petrified and left hanging on the second floor corridor alongside a warning that the Chamber of Secrets had been opened. Filch was devastated by this, initially suspecting Harry Potter and wanting to see punishment. For many months afterwards he guarded that spot and was more miserable than normal. She was restored using Mandrake Juice at the end of the year.
 Third Book
 Fourth Book
When Harry Potter went for a late night wander to try and work out the clue for his next Task in the Triwizard Tournament, he used the Prefects' Bathroom. On his way back underneath his Invisibility Cloak he was trapped in a trick staircase. Mrs Norris found him and Harry was worried that she could smell the perfumed bubble bath he'd used.
 Fifth Book
 Sixth Book
 Final Book
 Outward Appearance
She is dust coloured with yellow, lamp-like eyes.
 Personality and Traits
Mrs Norris does what Filch would want her to do, following around suspicious students (and Hagrid) and going to get Filch as soon as they do wrong. Harry Potter suspects she can see through Invisibility Cloaks, though it is probable that she tracks using scent.
 Additional Canon
In response to suspicion that Mrs Norris was more than she seemed and could be an unregistered Animagus, J. K. Rowling responded on her website, saying: "No, she's just an intelligent (and unpleasant) cat."