Shelley Marsh is Randy and Sharon Marsh's daughter and Stan Marsh's older sister. She is ill-tempered and aggressive, referring to those around her as 'turds' and often beating or even torturing Stan when adults are not around, though nonetheless compassionate; later seasons have instead emphasized her as assertive and focused more on her relationship with her father. She has been voiced at different times by Mary Kay Bergman, Eliza Schneider, and currently April Stewart. She first appeared in the Season One episode, 'An Elephant Makes Love to a Pig'. At the time of her introduction in 'An Elephant Makes Love to a Pig', it is established that Shelley has been physically harming Stan for some time and that the other boys are already aware of it, questioning if she caused his black eye. Stan insists that she has been beating him up because she recently received orthodontal headgear at the dentist and is taking her anger out on him, and throughout the episode she questions if he is staring at her headgear or her neck brace, accusing him of lying when he denies this and using it as a pretext to attack him. These attacks including elaborate setups such as throwing him through a window and trying to use a lawnmower on him. Stan insists that their parents have not listened when he has previously tried to tell them she is beating him up, and that they don't believe him. They take Shelley at her word that Stan has been with her despite being told by Uncle Jimbo and the news that Stan has been attacking the town, an act which establishes some mutual understanding between them, though she continues to attack him. (Source: Fandom.com, CC BY-SA)