Madison is a character seen in flashback in Chapter 8 of The Good Place.
She is rich, rude and cranky. She was Eleanor’s roommate when Eleanor was alive. She was victim to Eleanor and her other roommate in the ‘Dress Bitch’ business after an argument and law suit with the dry cleaners after Eleanor wore the dress without permission and ripped it. It was only when Eleanor decided to confess Madison knew that she was responsible for the Dress Bitch.
In the second timeline when Eleanor is trying to be good, Eleanor admits that she and Brittany were behind the "Dress Bitch" shirts. Madison storms off in rage and moves out.