Jimmy is friendly and thoughtful and likes helping out around the Professor's lab. Like his cousin, Spike, Jimmy is simple-minded and prone to accidents, such as inadvertently sending a shipment of Pipo helmets to the monkey park (causing the monkeys to regain their intelligence and evil intentions and single-handedly sparking the events of the game) and crashing vehicles.
Jimmy seems to lack the competitiveness and attitude of his cousin, but still possesses an immense tenacity and willingness to get things done. Jimmy is somewhat more emotional than Spike, and, although still possessing a willingness to fight in order to win, seems to prefer trying to settle things without fighting when possible, such as when he tried talking Specter out of his evil plans instead of outright attacking him ("Why don't you try doing something good for a change?").
He also seems to have both a fondness for and a way with animals and is rarely seen without the companionship of the baby monkey Pipotchi. When Jimmy left Pipotchi in the care of Natalie and the Professor (in order to continue his adventure without endangering him), Pipotchi soon fled the safety and comfort of the lab to return to being with Jimmy.