Jimmy is a violent and heavily brain-damaged man. His condition is the result of spending an entire day staring at the sun, which literally fried his brain. According to many characters (namely Dale), this is the cause of the man's apparent dementia, although he wouldn't have been too smart to do it in the first place. Or, as Dale put it "Kind of the chicken and the egg thing". In Ceci N'est Pas Une King of the Hill, it is revealed that Jimmy is inbred, which is likely the origin of his stupidity. Despite this, it is referenced in The Substitute Spanish Prisoner that he has exceptional counting abilities such as being able to count a box of toothpicks, this being a reference to the 1988 movie Rain Man which revolved around an autistic man with the ability to count incredibly fast and accurate. However, this was probably a lie as it was said by the con artist who created the genius scam.
Jimmy has been seen working at a variety of different jobs, most notably managing a concession stand at the race track. Bobby Hill briefly worked for him there. Jimmy initially treated Bobby badly, until he made him his "go to guy." Bobby told Hank that Jimmy was working him too hard, making fun of him, and calling him a moron. Hank ignored what Bobby told him, dismissing it as Bobby being a brat or trying to get out of having a job. However, Hank realized Bobby was telling the truth when Dale filled him in on Jimmy's back story. The last straw for Hank was when Jimmy told Bobby to bring a soda to him from the infield, nearly killing Bobby by ordering him to cross the track while a race was in progress. Hank, infuriated, ended up running across the track himself chasing Jimmy down and literally kicking his ass violently.
- Life In the Fast Lane: Bobby's Saga - First appearance where he was the boss at a concession stand at Arlen Raceway where he was kicked in the ass by Hank for trying to make Bobby give him a soda across the track.
- The Substitute Spanish Prisoner - Jimmy is accepted into a genius society, but it turns out to be a scam, rigged so that anyone can join (much to the consternation of Peggy Hill, who is also accepted into the society).
- Business Is Picking Up - Jimmy is seen bullying Peter Sterling, who owns and operates a very successful business which specializes in picking up animal droppings and cleaning out Port-a-Johns.
- Ceci N'est Pas Une King of the Hill - Jimmy makes art (little people made from beer cans) and is praised by art critics for it. However, when his work sells, he gets angry: "Don't take away my guys!" Jimmy is pacified when the art dealer sponsoring the show promises to give him more cans instead of money.
- When Cotton Comes Marching Home - Jimmy is seen with Cotton, along with Hank watching him and Cotton, getting the money from collecting cans from the manager at Pink & White's recycling center. Cotton disagrees and wants the money, saying that he is broke. Jimmy is seen again later in the episode when Cotton starts to show him "how to count" by throwing cans at him.
- Bill Gathers Moss - Jimmy is seen being interviewed by Hank and the others to see if he would be a good room mate for Bill, but during the interview, he said that he wants the house and a sign outside the front door that says "Jimmy's House".
- Lucky's Wedding Suit - Jimmy is in the lawyers office. He wants to sue somebody because he ate the warning label and choked on it.
- Edu-macating Lucky - Jimmy is seen taking a GED test when Lucky goes to take the test, which whom he is sitting next to, which Lucky says out loud remembering that the value of Pi R squared is 90210, which Jimmy tells him that he just gave away the answer, and covers his test from Lucky.