He and his brother Xavier are generally quite inactive, and constantly making note of how they are sitting in front of the digital tree in his backyard of the family, much to the chagrin of their sister Amanda.
His life takes a turning point, however, when by chance receives a visit from the age younger versions of his uncles, Phineas and Ferb. After the previous visit, Xavier and Fred build bumper cars that can move in five dimensions, but they still answer Amanda's questions about their activities with "Nothing", which bothers her to no end ("Phineas and Ferb's Quantum Boogaloo").
Xavier and Fred are as bright and creative, and build impossible contraptions just like Phineas and Ferb, although it took the younger version of their uncles to bring it out of them. Fred keeps talking about being next to something the few times he talks ("I'm sitting next to him", "I like the kid standing next to him")
Fred has blue eyes and brown hair. He wears a white shirt with a red vest covering it, white shorts, and red sneakers.
Fred and Xavier weren't interested in creating things, until Phineas and Ferb give them an idea to create 5th dimensional bumper cars.
Candace mentioned that in the future she will marry Jeremy and have two kids: Xavier and Amanda. Fred's inclusion is almost certainly intended as a play on this theme, which implies that, alternatively, Candace changed plans or had more children than she expected.
Unlike Phineas and Ferb, their mother (Candace) sees that they've created the 5th dimensional bumper cars, but when Amanda says "See Mom, they never do anything!" Candace simply says "Give it a rest, Amanda."
Like his uncle Ferb, Fred doesn't talk much and lets Xavier do most of the talking.
Despite his mother having red hair and his father having blond hair, he has brown hair.
It is likely that he could be adopted if Candace planned to only have Amanda and Xavier as her biological children.