Like Vicky, A.J.'s last name is unknown. Also, it's unknown what his initials, A.J. stand for until it was confirmed in A New Wish that his name stands for "Anthony James".
He is the only African American main character and the first overall following Hazel Wells
While A.J.'s family is obviously well off, he is not considered among the popular kids, possibly because of his high intelligence and because of his friendship with Timmy and Chester.
He is prematurely bald and is not happy about it, as evidenced by Fairy Idol and Wishology.
He lives across from Chester in front of some railroad tracks as shown in The Big Scoop!
A.J. has successfully cloned himself. A sleeping clone suspended in a tube can often be seen in his bedroom (which he is hiding from his parents), and a number of identical clones were featured in The Jimmy and Timmy Power Hour.
In It's a Wishful Life, it's revealed that if Timmy didn't exist, then A.J. would have a full head of hair and already be enrolled be in college.
In the first two seasons, A.J. was voiced by Ibrahim Haneef Muhammad. He was replaced with Gary Leroi Gray, starting in Season 3. Gray's last episode voicing A.J. was in the Season 9 episode, App Trap. In A.J.'s next (and final) speaking role, Dimmsdale Tales, he is voiced by Rickey D'Shon Collins.
In Girly Squirrely, he was voiced by Grey Griffin and was referred to as "Panicky Scout" in the credits. He just sings the Squirrely Scout credo and then later shouted "Stinkfoot!"
A.J. (along with Chester and Francis) was originally going to be in The Bored Identity but were scrapped for unknown reasons.
In a video on creator Butch Hartman's YouTube channel, he remarks that A.J. (along with Chester and Trixie Tang) had fewer appearances as the series went on because, while they were important early in the series, this was no longer true as the series went on. In Season 10, he was replaced as the only A-student in Timmy's Class by new character Chloe Carmichael. Unlike A.J. however, Crocker openly reveres Chloe for her intellegence, whereas he showed open disdain for A.J..
AJ along with Timmy, Cosmo, Wanda, Mr. Turner, Mrs. Turner, Chester, Jorgen, Mark, Chet Ubetcha, Mr. Crocker, and Vicky are the only characters to appear in every season of the show.
However, he, Chester, Mark, Vicky, and Chet started having minor roles in the later seasons.
The Big Scoop is the only episode to solely focus on him and Chester without Timmy.
Quotes
"It's Tuesday; on Tuesdays we multiply fractions for dessert. Nothing is sweeter than knowledge."
"No man can own the Internet! I'd know, I've tried!"
"Thank you corrective dentistry!"
"You know, despite the pain involved in playing Timmy Ball, I find it gratifying to see everyone in the neighborhood enjoying themselves as much as we are."
