Main characters • (voiced by Laurence Bouvard) – The titular character and
protagonist who is best friends with Tommy Turnbull. He is a robot created by Professor Moshimo as a force to protect the world from threats after Protoboy failed, as he was captured and reprogrammed by Dr. Kamikazi. Robotboy was sent to live with Tommy for his own protection. • (voiced by
Lorraine Pilkington) – Robotboy's 10-year-old owner and human best friend. He acts as a role model and mentor figure to Robotboy and cares deeply for him. Unlike Gus, he is bright, sensible, kind, and responsible, although he gets criticized by his father Dwight for being rather nerdy and not getting enough exercise. • (voiced by
Rupert Degas) – Tommy's goofy, naive best friend and brother. Despite coming from an Amish family, Gus is "the black sheep" of the bunch and is infatuated with food and video games. Unlike Tommy, Gus tends to be much more rude and self-centered in nature and it is usually this that gets everyone into situations caused by Dr. Kamikazi. • (voiced by Laurence Bouvard) – Lola is the 10-year-old daughter of African ambassador, Kingsley Mbola. She is confident and intelligent, being able to fly jet planes and control speed boats.
Supporting characters • (voiced by
Togo Igawa) – Professor Moshimo is the creator of Robotboy, Robotgirl, Protoboy, and Robotman. He received a letter from Tommy Turnbull about him looking forward to his latest invention. As a result, he sent him Robotboy to take care of. • (voiced by Laurence Bouvard) – Professor Moshimo's girlfriend and lab assistant. She is typically depicted as silent, however, she speaks for the first time in the episode "Grow No-Mo". • (voiced by Laurence Bouvard) – Robotboy's female counterpart and younger sister.
Villains • (voiced by Eiji Kusuhara) – A self-proclaimed evil genius and the main
antagonist of the series. He wishes to capture Robotboy to create a template for an army of super robots, with which he will be able to achieve world domination. • (voiced by
Rupert Degas) – A hunchbacked henchman of Dr. Kamikazi who also is a master of sumo wrestling. He is the secondary antagonist of the series. • (voiced by Rupert Degas) – Tommy's older brother and secondary archenemy, he is a constant bully to every child in the neighborhood, including Gus and Tommy himself. Some people exploit his attitude and poor intelligence for their benefit, usually Dr. Kamikazi. • (voiced by Rupert Degas) – A bully at Tommy's school who constantly bullies Gus and Tommy, as well as any other kid he finds. His dad is a government agent who has used Kurt to try and capture Robotboy. Tommy sometimes has outsmarted Kurt and his cronies by outwitting them, usually with Robotboy. • (voiced by
Lewis MacLeod) – A secret agent who strives to take Robotboy to reproduce him so he can use him for government means. His base is located in the
Transamerica Pyramid. • (both voiced by Rupert Degas) – Kurt's friends/henchmen. Stu is the largest and least intelligent of the group. He wears a blue hoodie with a red cap. Mookie is the smallest bully in the group, in the absence of Kurt, is the leader. • – A
queen bee-like character and Tommy's love interest. Despite being clearly out of his league and already having Kurt as a boyfriend, Tommy still attempts to get her attention despite being treated like he does not exist. • (voiced by Lewis MacLeod) – A
Nordic egotistical boy genius who is about Tommy's age and claims to be a greater genius than Professor Moshimo. He has his own robot double named Björnbot, who is sometimes referred to as Brother Björn. Their mission is to destroy Moshimo's creation—Robotboy, so Björnbot would be "the greatest fighting robot in the world". • – Björnbot is a robotic lookalike of his creator Björn Björnson. He has weapon capabilities and strength equal to that of Robotboy—as well as superactivation. Unlike Robotboy, he lacks emotion and has a flat vocabulary (which consists mostly of the word "Ja!"). • (voiced by Lewis MacLeod) – Robotboy's long-lost brother, who was created by Moshimo in his earlier years. He was later taken by Dr. Kamikazi and Constantine and reprogrammed, forcing him into evil. • (voiced by
Rupert Degas) – A wealthy man from Germany who wants to use Robotboy's parts to replace his own. Affenkugel is frail and has been mistreated since childhood because of his condition. • – An orangutan who is Affenkugel's assistant. • – A magician who had his career ruined after getting ridiculed and humiliated by Gus during a performance. He is always ready to get back at Gus and/or possibly kill him given the chance. • (voiced by Lewis MacLeod) – Tommy's principal and nemesis. She abuses her position as principal to confiscate toys and play with them herself, having been denied toys as a child. • – A janitor who is Friedman-Culpepper's henchman. • – A yak who was made fun of due to his low intelligence. Professor Moshimo gave the yak a brain transplant to enhance his intelligence, which resulted in him being ostracized even more. After disappearing for a few decades, Brainy-Yak returns, seeking revenge for being excluded and being mistreated by Moshimo. ==Reception==