Mrs Norris
Background
Mrs Norris is Mr Filch's cat.
During the events of Harry Potter and the Sorcerer's Stone (2001)
The staircase moves as Harry Potter, Hermione Granger and Ron Weasley are walking up it and as they go to leave a room they aren't supposed to be, they see Mrs Norris and run away.
During the events of Harry Potter and the Chamber of Secrets (2002)
During the school year, Mrs Norris is petrified by the Basilisk. Later, those who were petrified recover.
During the events of Harry Potter and the Prisoner of Azkaban (2004)
The Fat Lady in Painting disappears from the common room portrait. Albus Dumbledore arrives with Mr Filch, who is holding Mrs Norris, and Dumbledore tells Mr Filch to round up the ghosts to search for the Fat Lady.
During the events of Harry Potter and the Goblet of Fire (2005)
Mrs Norris sits next to Filch as he plays the record before Professor McGonagall teaches the students how to dance.
During the events of Harry Potter and the Order of the Phoenix (2007)
Mrs Norris watches as Filch places increasingly more and more of Dolores Umbridge's rules on the wall.