Mary Knowles was a character in House of 1000 Corpses and got a small mention in The Devil's Rejects.
Mary is Bill Hudley's girlfriend. She, along with the other teens, takes Captain Spaulding's Murder Ride. As Jerry Goldsmith wants to find Deadwood, they drive into the night, trying to find it. While driving, group stops to pick up Baby Firefly and take her home. Rufus shoots out their tire, and Mary, along with others, takes temporary refuge in Firefly family's house while their car is getting fixed. She dislikes Baby, calling her a nut, a whore and a slut due to the fact that Baby flirted with Bill. In her rage with Baby, Mary leaves the house with the others, but is soon captured by Tiny. She is shown Bill's mutilated corpse, 'Fish Boy', by Otis B. Driftwood. She is chained up in the shed with some previously killed cheerleaders, and the sight of Mary and the dead bodies cause Don Willis and Steve Naish to panic before they are eventually killed. Mary, Jerry and Denise Willis are later about to be taken to Dr. Satan, but Mary manages to escape. After asking a permission from Otis, Baby runs after her and catches her, stabbing Mary many times, eventually killing her.
She was mentioned in The Devils Rejects as one of Baby's victims by Sheriff John Quincy Wydell during the torture scene. Captain Spaulding tried to take the blame, but Mary's picture is stapled to Baby's chest after Baby kept saying "she was mine".