He and his brother Fred are generally rather inactive, and constantly like to make note on how they're just sitting in front of the digital tree in their family's backyard, much to the annoyance of their sister Amanda. Their life takes a turning point, though, when they by chance get a visit from the younger-aged versions of their uncles Phineas and Ferb. After the aforementioned visit, Xavier and Fred construct bumper cars that can move in five dimensions, but they still answer Amanda's query about their activities with "Nothing" ("Phineas and Ferb's Quantum Boogaloo").
Xavier and Fred are as bright and creative, and build impossible stuff just like Phineas and Ferb, although it took the younger version of their uncles to bring it out of them.
Xavier looks quite similar to Jeremy Johnson, having blond hair, bright blue eyes, and a similar face shape. He wears a white T-shirt with brown stripes and green shoulders, green pants, and red sneakers with white lining. It was later confirmed by Dan Povenmire that Jeremy and Candace end up staying together, thus confirming that Johnson is the father of Xavier.
"Amanda" and "Xavier" are the two names that Candace had picked out for her future children. Given her interest in Jeremy, it's possible that he is the father of both children. This was later confirmed by Dan Povenmire during the 2015 San Diego ComicCon convention.
His, Fred's, and Amanda's situation is analogous to Phineas, Ferb's, and Candace's except rather than trying to "bust" her brothers for doing something, Amanda tries to bust Xavier and Fred for doing nothing. This being the case, Xavier is the Phineas of the pair as he talks more and he even tells that Fred that he likes Phineas while Fred responds that he likes Ferb.