Brad is a young boy with light skin, and light-brown hair, which is kept in a very short buzzcut. He wears black square glasses. He wears a cream-colored shirt underneath an unbuttoned green jacket, olive colored pants and black sneakers over light blue socks. He also wears a red cape.
"Danger's not my middle name... it's Scott" is what he says at the start of I Am Amelia Earhart. Also at the end of the same episode he says "mine's Scott" after Amelia reveals her middle name is Mary.
The international Xavier Riddle website reveals his last name to be Meltzer, proving that he’s a self insert.
Brad tends to be the most nervous and neurotic of the group. He is sometimes hesitant to go on adventures. Brad is quite partial to butterflies, as well as action heroes. Time traveling makes him temporarily dizzy; the further back the three go, the dizzier he gets.
He is described as having “delusions of averageness”, and is apprehensive over everything. His friends, Xavier and Yadina, encourage him to live a little and to try new things.
Apart from being neurotic, he's also very shy. He has a hard time making friends, and it's implied that he didn't have any friends prior to meeting Xavier and Yadina.
In I Am Susan B. Anthony, Yadina remarks to Brad "we're just used to looking after the Secret Museum ourself" indicating that the 3 kids did not discover it together: in the past Xavier and Yadina had tended it alone prior to inviting Brad to join them.
In concept art, he was originally bald and had round glasses and a scarf instead of a cape.
At https://pbskids.org/xavier if a browser clicks the picture of him hanging from a rope enough times he will say "doesn't matter WHERE or WHEN we are, I'm always, ALWAYS allergic to cats"
Another character whose middle name has been revealed while their surname is still unknown is "Penny Ruth" of Inspector Gadget.
although he did not blush, "dreamy sigh" is how captions describe his reaction to watching Anna Pavlova dance before he says "she's incredible". It then cuts to showing him clasping his hands while his mouth ~warbles~ emotionally.
At the start of I Am Tomioka Tessai he is showing Xavier and Yadina a dreidel (a Jewish toy) he inherited from his father.