Jim Rennie, Jr., better known as Junior Rennie, is the secondary antagonist of the Stephen King novel Under the Dome, and the son of the novel's main antagonist James "Big Jim" Rennie. He is a small town thug.
Under The Dome
Since Dome Day, he is deputized, and he recruits new police officers for his father. Junior gradually devolves from a thug to a bitter, angry sociopath, suffering from a brain tumor disguising itself as migraines. He particularly hates Dale Barbara, who laid a beating on Junior and his friends even though they outnumbered him. Dale could have had Junior arrested for assault, but Dale was an outsider and Junior's father was Big Jim. Junior murders Angie McCain early in the story, and Angie's friend Dodee Sanders a short time later when she stops by the McCain house. He later molests the corpses of the two women, referring to them as his "girlfriends" in his delusional state. He slowly becomes more delusional as the novel progresses and his tumor becomes more debilitating. Eventually Junior comes to the conclusion that Barbara has poisoned him and sets out to kill him. He later murders special deputies Stacey Moggins, Rupe Libby and Mickey Wardlaw by shooting them, before being killed himself by Jackie Wettington.
In the TV show version, Junior was portrayed by Alexander Koch. Like the novel, he started out as a psychopath and locked Angie McAlister (who ended her fling with him) in the fallout shelter for several days. Unlike the novel, however, he and his father didn't get along well since his mother's "death". He almost killed his father when he learned the truth about her mother's "death", but killed Big Jim's rival, Ollie. Ever since, he didn't want to hear his father's upcoming lies. He soon became the fourth hand of the mini-dome alongside Angie, her brother Joe, and Norrie Calvert-Hill. Before her death, Junior's mother painted a picture of her son in the yard with pink stars in the sky, equivalent of the phrase, "The pink stars are falling in lines." In Exigent Circumstances, his personality is conflicted by his involvement with the dome and Big Jim's trustworthiness. In the Season 1 finale, Curtains, Big Jim privately confessed to Junior that he killed some people and framed Barbie for those crimes. At the end of the season, Big Jim orders Junior to pull the lever to release the platform in hanging Barbie while Junior hesitates as the pink stars cover the dome and engulfs it into bright light leaving their fates uncertain. When the dome became magnetized and Linda sacrificed herself to free Barbie, he turned against his dad and vowed to kill him. When Angie was murdered, Junior was heartbroken. A few days later, he learned from Barbie that his uncle Sam Verdreaux murdered Angie and when Sam, Barbie, along with Pauline Rennie who turns out to have faked her suicide returned to Chester's Mill via the red door, Junior in a fit of rage tries to kill Sam, but pulled himself together and let him live. In the Season 2 finale, when Pauline was stabbed by her ex-boyfriend Lyle Chumley who Big Jim later killed, he tries to compose himself unlike his dad. After Pauline requested Rebecca Pine to inject the morphine into her body so that she could die, Big Jim bludgeoned Rebecca to death and went on a rampage. When Big Jim chased Julia who witnessed him murder Andrea Grinnell, Junior shot his dad and presumably left him to die while the dome was shrinking. Junior caught up to a winded Julia who could not leap across the chasm due to her wounded leg and waited for Barbie to come back to them when he and the rest of the town-members presumably found an exit from the dome.
In Season 3, Junior was infected by the egg's power and was part of the Kinship lead by Christine Price. In the series finale, when the dome came down he tackled his father trying to stop him from shooting Dawn. Just when it looked like he was going to kill him, Big Jim's new dog, Indy, distracted Junior giving Big Jim the advantage and he fatally stabbed Junior with a knife and Junior died in his father's arms.
- His literary and television counterparts shares many similarities, such as being a thug, recruiting new officers for both forces, and doing crime. He seems to have turned a positive direction in the television series (in helping the three other teenagers to figure out what the dome is all about and protecting people close to him) instead of turning in more of negative direction in the novel, where he kills Angie McCain, Dodee Sanders, and three special deputies.