Tommy Turnbull is a blond, square-headed boy, and Robotboy's caretaker. He is smart, responsible, sensitive, likable, and acts as a mentor to Robotboy. Tommy tries to teach Robotboy the ways of the world through his eyes. He is the son of Debbie Turnbull and Dwight Turnbull, and the little brother of Donnie Turnbull. He is the unofficial leader of the team.
He was voiced by Lorraine Pilkington.
Robotboy is Tommy's best friend, and they have been accompanied in many adventures which improves their attachment. In many episodes, he teaches Robotboy about humanity and behavior, being a very special mentor to him whenever he needs explanations.
In the episode "Robot Rebels", Kamikazi broke their friendship with his disguising plan, but thanks to Tommy, they reunited again. In fact, there are many times in which countless villains have broken their friendship and, after an explaining, their friendship is attached again.
In the episode "Crying Time", Dr. Kamikazi reprogrammed Robotboy to do and obey his bidding, and his bidding was to destroy Tommy. But after Robotboy seeing Tommy cry for mercy, he remembers one of his moments with Tommy and doesn't destroy him after all.
Donnie is the older brother of Tommy. Donnie usually bullies Tommy. Despite this, Tommy still treats Donnie like family.
Lola is the confident and smart ten-year-old daughter of a rich African ambassador, and one of Tommy's best friends. She also secretly has a huge crush on him, which Tommy does not seem to realize. Tommy also gets annoyed whenever someone calls Lola his girlfriend, though he won't accept her true affections towards him.
Gus is one of Tommy's best friends, even though Gus constantly takes advantage of him and sometimes acts selfish. He won't think twice about stealing from Tommy and abandoning his friend for his own sake. Still somehow they remain friends and Gus does occasionally help the team out of a jam.
Dr. Kamikazi and Constantine are the main villains the the show, although Donnie (his big brother), Kurt, and Special Agent have become a big threat to Robotboy in the series.
- The main reason why Tommy got to be the keeper for Robotboy is due to Tommy being Professor Moshimo's biggest fan, therefore it is likely that Moshimo is able to trust Tommy because of this.
- Along with Robotboy, Tommy has appeared in all the episodes of the series.
- Tommy is the only member of his family where his name does not start with the letter "D".
- Tommy gets frustrated whenever someone calls Lola his girlfriend, very much like in Chowder, when Chowder keeps telling Panini that he's not her boyfriend.
- Donnie can get on Tommy's nerves, as shown in "Up a Tree".
- His appearance is loosely based on Mac (Foster's Home for Imaginary Friends), because of his square-shaped head (and, coincidentally, also has a nasty big brother like Mac's big brother Terrence).
- Tommy was the first character, apart from Professor Moshimo, to have mistakenly called Gus "Goose".
- Tommy Turnbull's name maybe a reference/homage to Timmy Turner from The Fairly OddParents.
- Tommy has been able to meet his idol The Human Fist twice.
- In "Nursing a Grudge", Felonious Hexx had called Tommy "Tommy Turntail" upon meeting him.
- He is female in the Chinese, Korean, Japanese, Vietnamese, Mongolian, Kazakh and Kyrgyz dubs of the series.
- He has a crush on his schoolmate Bambi, but not Lola, despite Bambi constantly bullying Tommy.