T.J. is a short, chubby (moreso in season one), freckly boy who is almost never seen without his red baseball cap (which he always wears backwards). He wears a green jacket with a white T-shirt from inside and blue jeans. His eyes are noticably bigger than the other characters. According to the creators, his eyes are blue, though this was never shown on screen. He also had highlights in his eyes in season one, however they were removed in season two. This may be because he was the only character with the highlights and it looked strange compared to the others, or because the artists forget to draw them in a number of shots, so they were just removed.
His personality is generally mischievous and kindhearted. He loves playing pranks on teachers (Mostly Ms. Finster or Principal Prickly). TJ also has a strong sense of honor, fair play, courage, selflessness and compassion. He is the man with the plan, and most of them succeed in the end. He also has a big heart, and cares about every kid on the playground, even the ones he considers his antagonists.
Despite these traits, he is still not without his flaws. Although he is a genius at designing his plans and pranks, he's also lazy and doesn't do very well in school, which is played out more in later episodes. Although this comes more out of his laziness and indifference rather than actual stupidity. He is also a bit of a piggish eater, as seen in a few episodes including "Omega Kids", where he has fifteen slices of pizza for lunch and then asks Vince for another slice, and in "A Great State Fair", when he mentions that his plans at the fair are eating all the junk food he can find. This was also hinted in his earlier character page on Disney's website, where he mentions his favorite foods are "anything and everything, except the tomato surprise they serve in the cafeteria".
His favorite sport is kickball and plays it nearly every single episode. It has been hinted at in several episodes that he has a crush on Spinelli, most strongly in The Experiment, and is somewhat confirmed in "More Like Gretchen" when he tells Spinelli that "his heart goes out to her". One of his dreams is to be an astronaut, going around the galaxy for high adventure.
In the future TJ will become 5'9 as predicted by Galileo.
His parents are very loving and supportive. They don't always appreciate the full extent of T.J's high spirits, but they love him just the same. TJ's relationship with Becky is on much shakier ground, but underneath all her objections to her brother she does love him too, even coming to his rescue in Recess: School's Out. In The Great Jungle Gym Standoff, TJ reveals that he also has an older brother.