In J. K. Rowling’s Harry Potter and the Prisoner of Azkaban, Gryffindor Tower’s portrait guardian is the Fat Lady.
The Fat Lady’s portrait conceals the entrance to the Gryffindor common room. Students must give her the current password before she swings open, allowing them to pass through the portrait’s opening. She is one of the recurring magical details that makes Hogwarts function like a living school.
During the third novel, Sirius Black attacks the portrait after apparently trying to enter the tower. The damaged portrait is temporarily replaced by Sir Cadogan, a dramatic knight who challenges students and changes passwords frequently. The Fat Lady later returns to her position.
The Fat Lady is easy to confuse with the Grey Lady, who is the ghost associated with Ravenclaw House. She is also distinct from the Bloody Baron, the ghost of Slytherin House. The novel was published in the United Kingdom in 1999.