Mitch Connor is the name of a con man who possesses Eric Cartmans hand on two occasions. Cartman is shown to truly think he is real, as he talks to Mitch when alone; Mitch even " sleeps " with Ben Affleck while Cartman sleeps. At the end of Mitches first appearance in " Fat - Butt and Pancake Head ", Mitch apparently commits suicide by taking a cyanide tablet, but appears again in " 200 " and " 201 ", trying to get money by selling Muhammad's Goo, once again under the guise of Jennifer Lopez.
Cartmans unhealthy mind could have made up Mitch and believed him to be real out of a desperate attempt to have a friend who wouldn't insult, one who he could have total control. However, Mitch says things that conflict with Cartman, they argue when alone, Mitch does things that Cartman is most likely unaware of ( like sleeping with Ben Affleck ), and Mitch even has memories of his own, such as his being in The Vietnam War.
In " Volcano ", Cartman says that he was in Nam, meaning Vietnam; this could be Mitch Connors influence on Cartman and the time when Mitch first enters Cartman, or just the birth of Mitch through Cartman. Mitch could the soul of a man who went into Cartman for an unknown reason, and slowly got stronger until he took control of Cartmans left hand. The reason for Mitch not nearly killing Cartman like Kenny did could be because Kenny has a background leading to Cthulhu, while Mitch is just an ordinary spirit. Spirits have been seen before, making it possible that Mitch is a spirit.
Mitch does not appear in The Imaginationland Trilogy; if he was imaginary, something made up by Cartman, then he should have appeared, unless he just wasn't seen. Mitches lack of appearance, on both the good and evil sides, means that he was not imagined by Cartman, meaning that Mitch is in fact a real person.
In the latest episode, " 1% ", Cartman is shown to be extremely unstable; he kills all of his Stuffed Animals one by one, not realizing it was in his own delusion scenario. He believes that Polly Prissypants is responsible for the murders when she reveals herself, and even talks to her when he thinks he is by himself, showing that he may in fact truly believe that his Stuffed Animals are real. This lack of mentai health shows that Mitch Connor could in fact a delusion created by Cartman. This begs the question as to why none of these imagined personalities showed up in Imaginationland. It could be due to his not actually Imagining them, but were in fact extensions of himself. The same could be said for Mitch Connor, and even his arguing with Mitch could help insist that Mitch is a creation of Cartmans.
If you look at Cartman's relationship with Butters and Kyle, you'll find similarities between them and his percieved to be imaginary friends. Butters is like Cartman's Stuffed Animals, who will always, almost always anyway, agree with him and never out him down. Butters made Cartman realize how much he missed Kyle being around, someone who would bring some excitement into his life, even if it was by insulting him and ruining his plans. Cartman went on to save Kyle from dying in San Francisco, just so he could have him for the excitement. Kyle and Mitch Connor are also similar; Kyle challenges Cartman, and Mitch Connor will try to make Cartman do things he wouldn't want to do, such as steal Muhammad's Goo and sell it, after Cartman gets fed up with the plan. Mitch Connor, unlike the other percieved personalities, has a mind of his own, and seems to be friends with Cartman, a friend who is like Kyle, giving him a challenge, but also a friend who won't insult him for no reason.
I think Mitch Connor is a real person, one who has somehow survived after death and lives in Cartman's when he feels he needs to, and when he wants to.