At the end of Operation: T.R.E.A.T.Y. the two mysterious figures seen spying on Numbuh 1 throughout Season 6 are revealed to be Numbuh Infinity and Numbuh 74.239. However, Numbuh Infinity was never seen after this and only Numbuh 74.239 returned in the series finale, Operation: I.N.T.E.R.V.I.E.W.S..
In Morgan's universe, she didn't know his name was Gabe so she named him Billy, but she's thinking of changing it.
His last name is Quarks, which is a sub-particle of a proton.
In Gamewizard's universe, his name is Gabe, and he is an alien being called a Wisp, and has been alive for hundreds of eons. He and Numbuh Infinity come from Planet Wisp and are great friends with Jirachi. When Planet Wisp was destroyed, he and Infinity were the only ones that survived. When the Irken Empire took control, they were the only ones to escape with Jirachi and crash on Zathura, where they met Dimentia and eventually started the GKND. Since then, they worked with Dimentia, and she normally sends them on missions down to other planets to recruit more operatives, often changing them into the form of the inhabitants of that planet, so as to blend in.
In the one-shot "Break", Numbuh 14 tried to get Gabe to take a break from doing his homework.
In the future, Gabe is married to Numbuh 14 and has two kids, who both work for Sector N.
Gabe has orange hair, light-blue eyes, buckteeth, and freckles on his face. He wears a white lab coat with a blue shirt underneath, and big brownish-gray pants. He wears black shoes with white socks.