Agatha Faversham was an elderly woman who hired the Ghostbusters to deal with the Thing in her attic.
Agatha Faversham’s father wanted her to have a perfect life, even though she was pretty much content with her life when she was young. The Thing that was summoned by her father was too powerful for him to control, so he imprisoned the entity in the attic and told his daughter never to go in there. He even forbade her from going up when she returned home after her husband passed away. She honored his last request: never sell the house and never go into the attic.
70 years after she was first forbidden, Agatha Faversham still heard strange noises in the attic and decided to call the Ghostbusters in order to get rid of them. Agatha remained at the Firehouse while the Ghostbusters investigated. After the Thing was defeated by the Ghostbusters, Peter Venkman offered to spend some time with Mrs. Faversham because she reminded him of his mother, who was alluded to being deceased.