T.J. is the leader of the main six kids in the show and has been best friends with them since kindergarten (except Gus, who moved to town in the first episode, however, he has also been shown in kindergarten with the rest of the kids). He is outgoing, kindhearted, optimistic, and friendly, and takes having fun very seriously. He is also very dumb, and once he even scored a 10% on a test. While he is somewhat ditzy, ignorant, and lazy, he's a genius when it comes to pulling schemes on the playground.
Despite being more heavy-set than the other five members of the gang (save for Mikey), he is capable of pulling a few stunts, such as escaping detention by climbing either out the window or from the roof of the school a few times. In second grade, he invented the word "whomp", which is what the kids of the playground use instead of "stinks" or "sucks" to describe an unpleasant situation or person. Aside from "whomp", he also uses the word "frooping" a number of times (to replace the "f-word"), though it is unknown whether he created the word or not. T.J. often roots for the underdog and cares about every kid on the playground, including his enemies. Thus causing most of the school to like him, with the exception of Gordy, as seen in the episode, "Nobody Doesn't Like T.J.". He is hardly ever seen without his red baseball hat.
His best friend, Ashley Spinelli, has a crush on him, as revealed in the episode "Parents' Night". In the episode "The Experiment", they kiss each other to experiment on the effects kissing has on the opposite genders, with them seeming to not enjoy it. However, when they are left by themselves afterward, they both seem to act a little shy about it, hinting that T.J. has a crush on her as well. He is often seen wrapping his arm around her shoulders for no apparent reason, which also hints this.
He was very shy as a kindergarten student and was not the brave leader that has been seen in the fourth grade. Gus was the first one to really become his friend, and he was also the one who gave him his nickname. After Gus proves to the other students that Mikey wasn't a bully, the other kindergartners start to become more outgoing and show the first displays of their usual personalities, When Randall tattles on Gus and is put in the principal's office, T.J. assumes his position as the leader when they have to save Gus, and puts his trademark baseball cap on backward as he wears it in the series proper.
In the original drafts of the show, his name was going to be P.J., to stand for the first initials of the show's creators (Paul and Joe). After the first recording for "The Break In", his name was changed for unknown reasons. His name was most likely changed to avoid confusion with the character of P.J. Pete from Goof Troop.
He has had the most voice actors out of the main six characters in the show. Ross Malinger played him for all of Season One and a few episodes of Season Two, ending with "Outcast Ashley". Starting from "The Game", Andrew Lawrence played him due to Ross Malinger going through puberty and no longer sounded like T.J., and played him until the end of the series. In between the last episode of the show ("Lost Leader") and the direct-to-video movies (Recess: Taking the Fifth Grade and Recess: All Growed Down), Andrew Lawrence went through puberty and was replaced by Myles Jeffrey for the movies. When the Lilo & Stitch crossover episode "Lax" aired, he had been replaced by Axel Alba. Both Axel Alba and Myles Jeffrey played T.J. in various TV spots for the show when airing on Toon Disney.
In the Italian dub, T.J.'s favorite show is mentioned to be Darkwing Duck.
According to Paul Germain and Joe Ansolabehere, T.J.'s described being "a funny looking little guy with a lot of charisma".
According to "Big Ol' Mikey", in his adult years, he will grow up to be 5 feet 9 inches tall.
T.J. has had the most episodes focused on him out of the entire cast.
T.J. has been in every episode of the series.
T.J. and his friends were originally going to make cameos in Lloyd in Space.
During the first season of the show, T.J. had highlights in his eyes. For unknown reasons, they were removed in season two but sometimes appeared in either off-model moments or tie-in merchandise.
T.J. is one of three members of the gang with siblings (along with Spinelli and Vince), however, he is also the only member of the gang with a sister.
The first line spoken by T.J. in the show was "Tomato Surprise; just when you thought it was safe to go back in the lunchroom". This is also the first line spoken by any character in the show.
In some early concept art (Using the finalized character designs), T.J.'s sneakers were gray instead of red, his eyes were also completely circular instead of being semi-circular, and his hair was blond instead of light brown.
T.J. was the first animated character that Ross Malinger and Andrew Lawrence have played.
In Japan, T.J. seems to be a fan-favorite; he is commonly seen as the show's mascot and is apparently considered an example of a "moe" character.
T.J. bears a strong resemblance to Ralphie Tennelli from Scholastic's The Magic School Bus.