Bowser Junior is a member of Team Fortune Street.
Bowser's son. He can be summed up as a bold and energetic troublemaker. He inherited his father's short temper and bad attitude. He is also bratty, spoiled, and rude. His favorite hobbies are stealing cookies, causing trouble for people, and scribbling. However, he seems determined to defeat Mario in a fair fight in order to prove his power. He is also occasionally lazy due to riding his Junior Clown Car. He's also apparently quite bright, being brainier than his father. He also has a habit, when energized or excited, of jumping from one foot to the other. In fact, he seems to have a hard time standing still for very long, suggesting he’s hyperactive. His selfishness can also work against him. He absolutely hates losing, and usually accuses his opponents of cheating or simply winning through luck. This also extends to how he sees his opponents. As a result he craves the respect and acknowledgment of others—especially his father—and resents being looked down upon because of his age or size. He's quite fearless when attacking his father’s enemies, although even he can be frightened into retreating when things go disastrously wrong in battle. In particular, he seems to have little to no fear of heights, and enjoys doing dangerous stunts on his airborne vehicles like standing on the rim of his Clown Car’s cockpit or balancing on the bowsprits of airships. He also seems fascinated by big, dangerous machines such as robots, and mechanized vehicles which he often employs in his fights against Mario. He seems to have a hand in designing at least some of the machines he uses. However, he is also obsessive about little details in the things that he makes as well as never being quite satisfied with his own work. Sometimes he'll add details because he thinks they're 'cool' only for him to have second thoughts about their practicality. Despite his love of doing evil, Bowser Jr. does seem to occasionally flirt with the idea of being a hero. However, he may just enjoy the positive attention more than actually doing good deeds. Despite all of his arrogant personality traits, it’s also stated that he harbors a lonely side that he doesn't let other people know about. He also seems more willing to swallow his pride than his father. In Birdietalk Productions, Bowser Jr. loses the ability to become Shadow Mario, and will instead go into "Big Bad Graffiti Mode" should he use his bandana. Just as he did in his source material, Bowser Jr. likes to cause mischief, as demonstrated in a comic where he dared someone else to kiss a villainous character. He is shocked when said dare went in an unexpected direction.
Along with Patty, Bowser Jr. was the first character to win a season of The Challenge.