Elvin Cartman is Eric Cartman's bratty little cousin as well as Aunt Lisa and Uncle Stinky's son. Throughout his appearances he is referred to as "Cousin Elvin". He has made two appearances, one being in "Merry Christmas Charlie Manson!" and the other in "Cartmanland". In "Le Petit Tourette " Eric inadvertently tells Butters that he and his cousin have already touched wieners, it is not known if he was referring to Elvin or Fred.
Elvin wears red shoes and has curly dark brown hair. He is almost always seen holding or eating a Fudgsicle, with chocolate smeared across his face. Like most of the other Cartmans, he is obese. When he got smacked by Cartman, one of his eyes went white and started twitching.
Elvin uses catch phrases similar to Eric Cartman, such as "Sweet!" and "Kickass!", but in different context and usually blurted out.
In the episode, "Merry Christmas Charlie Manson!", when he finally finished his Fudgsicle, he began to throw a fit, demanding another, annoying Cartman; Cartman hits him in the back of the head, causing him to go into a sort of vegetative state and his right eye to dilate. However, by the end of the episode he is back to normal.
- "Merry Christmas Charlie Manson!" - Introduced as Eric Cartman's cousin and accompanies him to go to the mall to see Mr. Hankey. After the police find out that Charlie Manson is there, they pursuit him, the boys, and Elvin. Elvin drops his fudgesicle and crashes several police cars.
- "Cherokee Hair Tampons" - (Cameo) Seen in a photograph in the Cartman Residence.
- "Cartmanland" - Seen at Mabel's funeral.
- "I'm a Little Bit Country" - (Cameo) Seen in a portrait.