James Donnelly is the oldest of 4 brothers. He is a troublemaker and drug user, who is often involved in criminal activity, and known for making stupid decisions. When he was young, his leg was injured in a car accident in which a runaway car sped down the road and crushed his leg. (Jimmy does not know who was driving the car; only Tommy and Joey Ice Cream know that it was actually little Tommy.) He walks with a permanent limp from the accident. Jimmy believes he should be the leader of the Donnelly brothers but his constant flare ups from his temper causes people to believe him incapable. Therefore, they follow Tommy. This constant battle for being the alpha dog causes friction between the two brothers throughout the season. Jimmy is basically the village idiot who thinks he is the next Kingpin. Just like his brother Kevin he is always screwing up and just like Kevin Jimmy doesn't realize it. Instead he thinks he knows exactly what is going on and that he can handle any situation not realizing that if it wasn't for Tommy he would be dead many times over. Sadly Tommy is always protecting the village idiot instead of just letting Jimmy get himself killed.
[pulling up to the curb to pinch Jimmy for the truck robbery]
Detective Frankie Stein: Jimmy.
Jimmy Donnelly: Hey, Francis.
Detective Frankie Stein: How you doing tonight?
Jimmy Donnelly: Good. How are you?
Detective Frankie Stein: Oh, same old, same old. [Detective Calero puts handcuffs on Jimmy]
Detective Frankie Stein: Detective Calero, I want you to take note that the suspect is turning himself in voluntarily.
Detective Domenic Calero: Yeah, I see that very clearly.
Jimmy Donnelly: Not for nothing, but what am I turning myself in for?
Detective Frankie Stein: Jimmy, you boost a truckload of shirts, you get seen. That's unlucky. You walk around all day wearing the evidence, I can't feel too sorry for you.
Jimmy Donnelly: So, this is for the truck thing?
Detective Frankie Stein: You got something else you want to confess to?
Jimmy Donnelly: No, I'm good.
Tommy Donnelly: [after leaving the bar and heading into the alleyway] What's this, the truck you didn't steal, Jimmy?
Jimmy Donnelly: Tommy, lighten up!
Tommy Donnelly: Get out of the truck. The cop's here.
Kevin Donnelly: Come on, you know Jimmy can't drive!
Tommy Donnelly: Neither can you! Get out of the truck!
Tommy Donnelly: [noticing a police car has parked in front of the alleyway where the stolen truck is] Son of a bitch! Get back in the truck!
Jimmy Donnelly: Now I should get in the truck.
Tommy Donnelly: Get back in the truck.
Jimmy Donnelly: Hey, no banging on the machines!
Joey Ice Cream: What, it took my money!
Jimmy Donnelly: It's supposed to take your money!
Jimmy Donnelly: [after getting into the truck he stole] Hey Tommy, you like this shirt?
Tommy Donnelly: You ask me if I like that shirt?
Jimmy Donnelly: Yeah, 'cause I got a couple thousand more in the back.