Gadget Boy & Heather, also known as Gadget Boy, is a spinoff to Inspector Gadget that aired from September 10, 1995 to July 4, 1998.
The series revolved around the adventures of a young bionic detective named Gadget Boy, who was believed by some fans to be Inspector Gadget in his youth. The first season of the show was called Gadget Boy & Heather, while the second season was called Gadget Boy's Adventures in History.
- Gadget Boy ― Voiced by Don Adams and later, Maurice LaMarche. He is the titular protagonist who is a child cyborg programmed with the personality of an adult detective. He works for Interpol, but like Inspector Gadget, is incompetent, clumsy, and gullible.
- Agent Heather ― Voiced by Tara Strong. She is the titular deuteragonist and an Interpol agent who has many parallels to Penny. In Irish blood, she serves as the nanny, caretaker, guide, and friend to Gadget Boy.
- G-9 ― He is the tritagonist who is Gadget Boy's robotic canine companion. G-9 can transform into anything Gadget Boy and his friends need. He is the series' counterpart to Brain.
- Myron Dabble ― Voiced by Maurice LaMarche. He is an eccentric inventor with a Swiss accent who invented Gadget Boy and G-9. In each episode, he gives the gang at least 3 Dabble-ventions to help them solve their case. He has an unrequited crush on Heather.
- Chief Stromboli ― Voiced by Maurice LaMarche. He is an Italian police chief that tells Gadget Boy, Heather, and G-9 of their missions by reading his exploding fax tie. He is similar to Chief Quimby from the original series, except he suffers more accidents.
- Spydra ― Voiced by Louise Vallance. She is the main antagonist who has 6 arms and wears a pink spider-themed costume that hides her face with a mask. Her face is so hideous that anyone who sees her unmasked will turn to stone from the shock. Spydra has many evil plans, but they're always foiled by Gadget Boy and his friends. She has some similarities with Dr. Claw. Even her parting phrase of "I'll get you yet, Gadget Boy!" is comparable to Claw's "I'll get you next time, Gadget! NEXT TIME!!!".
- Mulch and Hummus ― Voiced by Maurice LaMarche. They are the secondary antagonists who are a pair of twin thugs that assist Spydra. A running gag has Spydra confusing their names, even though Hummus has a larger bottom lip and both of the twins have distinctly different voices. They are similar to Dr. Claw's M.A.D. agents, except they're the only criminals (other than Boris) who work for Spydra, contrasting Claw having a whole squadron of M.A.D. agents.
- Boris ― Voiced by Maurice LaMarche. He is the tertiary antagonist who is a talking, sarcastic, gluttonous, Russian-accented vulture and Spydra's pet. Boris is often abused and beaten by Spydra. Unlike M.A.D. Cat, he's never treated nicely by Spydra.
- Gadget Boy and Heather(1995-1996): Episode Guide
- Gadget Boy's Adventures in History(1998): Episode Guide