Jim is portrayed as a selfless, optimistic, intelligent, friendly and creative teenage boy. As a means to beat boredom, he and his brother devise outrageous activities throughout their afternoons, often participating in activities like toy design, piracy, engineering, restaurant management, and other things usually inaccessible to children. The most notable trait is his enduring optimism, along with his ever-cheerful demeanor he always strives to uphold. Even in the face of the most difficult challenges that confront him, he manages to maintain his composure and keep his outlook on the situation positive. Jim often uses his ability to boost the morale of those around him during phases of depression.
As a young teenager, Jim has a large amount of optimism. He pushes forward every time he makes a daily plan. This is what lets his plans succeed, as most kids and teens would simply give up once the plan calls for challenging tactics. Usually, Jim will see the bright side of life, and when faced with a challenge, Jim will simply find a way to get through it. Jim attempts to inspire others with his optimism. Mostly, he does this with his stepbrother Ryan and their older, Norman.
He has many friends, almost all of whom have participated in his nearly impossible plans. For example: going on an adventure to find a buried treasure, riding on a roller-coaster, and having fun at a beach; all of which his friends have done with him. Even someone like Bernard Barnathan, who might otherwise be an adversary, regularly participates in the plans and also attends their family's fishing trip. Jim has shown his kindness several times. Many of his summer plans are because he wants to help someone. Like for Anneliese's birthday, he created a beautiful fountain beside her pool. Another was when he helped Isaac find his missing glasses.
Jim is flustered when Anneliese shows signs of her affections for him. Jim has shown to be thankful for the emotions and intentions of those around him. It's for this shortcoming of his that he notices Anneliese's love interest for him not as obvious, along with Ellen's intention to get him grounded, in which Ellen fails. The greatest example is the fact that Anneliese has a crush on him and is not always obvious about it. Jim, however, knows it. Once, Anneliese cut a paper string while standing next to Jim that featured his face and hearts, and he thought it was cute. Another time, she tells him "You had me at our grandchildren", and Jim falls for it when she corrects herself to "steaks." His concept of romance is especially simplistic, missing the subtle complexities and figures it could be plugged into a formula. It is possible that Jim inherited this weakness from his mother considering how she ignores Ellen's often completely justifiable rants of the impossible endeavors he and Ryan would engage in and neglect to acknowledge the frustration Ellen would feel when she on one occasion found herself in her daughter's position. Jim has a very perky attitude, sometimes annoyed, and in some cases, has shown signs of exasperation was when Ellen ignored his warnings and put herself in danger. There have also been times Jim has shown to be dismayed or exasperated is when Santa proclaims Glendale naughty, when Garth's distraught wailing interrupted his morning, and when Ellen destroyed his X-ray glasses. He was agitated to a particularly high extent when on what came close to turning out as a pivotal event in his family's history when he learned of his pet cat Tomato's disappearance which was actually caused by Ellen.
There are many instances Jim has openly shown exasperation that can be listed, there have been many times Jim was well and truly enraged. The most noted was on the day of the Spring Equinox when Ellen refused to cooperate with him during a critical moment when he needed her to swallow her pride and settle with the chores that she was forced to do because she's grounded and she arrogantly tried to get out of it, Jim resorted to yelling at her in a startling outburst of rage to force her to get back to work. Another time was when Ellen tried to help the boys restore their brotherly relationship, (which she had messed up in the first place), and only made matters worse. Having enough, Jim yelled at her, then furiously disowned her as a sister, to which Isaac says "I always told her, "Don't ever make Jim angry. You don't like him when he's angry." and Jim replies, "You can say that again."
Jim is a slender boy with blue eyes and brown hair in an undercut and parted on the left and also has a rattail. He wears a light brown Henley shirt with three buttons vertically lined from the top, brown corduroy pants with a black belt and gray tennis shoes.
In the Winter he layers a light blue neckline sweater with dark blue trimming and cuffs, while his winter wear consists of a brown jacket with silver buttons, blue snow pants, brown boots, white gloves, a green cap, and a dark red plaid scarf. For swimming, his swimwear is a dark green pair of swimming trunks with orange trimming sported with dark yellow sandals. When he plays basketball, he wears a neon green and white tank top with the white mostly at the bottom of the top, short neon green and white shorts, white cleats and yellow socks. His pajamas are a solid brown pajama jacket and matching pajama pants with a white turnover collar, buttons and cuffs.