Final answer:
Bertha Mason is a character in the novel Jane Eyre who is locked in Mr. Rochester's bedroom due to her mental instability.
Step-by-step explanation:
In the novel Jane Eyre, Bertha Mason is a character who is locked in Mr. Rochester's bedroom in Thornfield Hall. She is Mr. Rochester's first wife, who is hidden away because she is mentally unstable and poses a danger to others. Bertha is depicted as a madwoman who occasionally escapes from her confinement, causing chaos and fear in the household. Her presence in Mr. Rochester's bedroom is a central plot point in the novel, as it reveals a dark secret about his past and the moral dilemmas faced by the protagonist, Jane Eyre.