Tubby is very dedicated and has a strong sense of right and wrong. This is illustrated in "Kindergarten Derby" when Tubby expresses his wish to show everyone that fat people are just as good as skinny people. He decided that people would appreciate fat people if he could win the derby, and so he dedicated himself to training with the help of Mikey. While he was training, he noticed how the other kindergarteners were being treated like cattle by the big kids. In response to this terrible treatment and as a tribute to his trainer, Mikey (who had been the only kid in the history of 3rd Street to not finish the race), Tubby's wish, as granted by King Bob for winning the derby, was to end the tradition of the Kindergarten derby.
Tubby also expressed a very forgiving nature in episode, "Here Comes Mr. Perfect", when he decided to forgive Jared Smith for out-burping him and break the lock-out on Jared that had been instigated by TJ for Jared being better than everyone else. He proved to be a leader in this instance as everyone else in the school decided to follow suit and befriend Jared as well.
He is voiced by Jason Davis, who also voiced Mikey throughout the series.