Inspector Gadget is a famous cyborg policeman with a seemingly endless amount of gadgets he can summon by saying "Go-Go-Gadget" then the gadget's name. The word "Gadget" is actually part of the name, as hinted at in some episodes. Although he has all this equipment, Gadget is ultimately incompetent and clueless (in a manner similar to the Inspector Clouseau character of the Pink Panther series), and overcomes obstacles and survives perilous situations by sheer good luck, with help from his faithful niece Penny and intelligent dog Brain who both must secretly help him solve each case. Even his gadgets often malfunction, which Gadget often deals with by exclaiming that he needs to get them fixed.
Inspector Gadget is the main protagonist and titular character of the series and movies. The clueless Gadget frequently bungles during his cases and gets into danger, but he always gets out of trouble through either his trusty gadgets, Penny or Brain's unseen assistance, or pure luck. One of his most famous catch-phrases in the series is "Wowsers!" While he would never succeed in completing a mission by himself without Penny and Brain, they usually would not succeed in completing a mission themselves without Inspector Gadget and his gadgets unintentionally foiling the MAD agents' plans.
Penny is Gadget's precocious niece. She is a master of investigation and technology who is the one truly responsible for foiling M.A.D.'s schemes, a fact only Brain knows. Using a computer disguised as a book and a utility wristwatch, she monitors her Uncle Gadget's activities, communicates with Brain and foils M.A.D.'s plots. Penny very often gets captured by M.A.D. agents before calling Brain for help or escaping by herself.
Brain is Inspector Gadget's and Penny's faithful pet dog and companion. He is bipedal, just as intelligent as a human and assists Penny in keeping Gadget out of danger and solving the crime. Brain uses a variety of disguises, which Gadget never sees through, and is often mistaken for a M.A.D. agent by Gadget. Brain's collar is outfitted with a retractable video communications system linked to a computer wristwatch Penny wears that allows her to relay information on Gadget's activity, or warn Brain as to the whereabouts of M.A.D. agents. Brain can communicate with humans, through a gruff, Scooby-Doo-like "dog" voice or pantomime and physical gestures to communicate effectively.
Chief Quimby is Inspector Gadget's short-tempered boss and the chief of Westfinster. He has a moustache and is usually seen with a pipe in his mouth. He appears disguised at the beginning of each episode with his own theme music to deliver Gadget his mission only to be blown up by the self-destructing message (a parody of the Mission: Impossible messages) because of Gadget's obliviousness; he appears again at the end of most episodes to congratulate Gadget on a job well done, but he never realizes that it is Penny who is truly the one responsible for foiling Doctor Claw's plots.
Corporal Capeman is a recurring character introduced in the second season as Inspector Gadget’s sidekick. Capeman is a self-proclaimed superhero who acts in the manner of a stereotypical crime fighter but, though more observant than the Inspector of details, is equally as inept at interpreting them. Capeman is obsessed with learning to fly and often mistakenly believes he has miraculously acquired the power of flight while in the midst of dire circumstances.
Doctor Claw (his real name is never revealed) is the main antagonist of the series and leader of the evil M.A.D. organization. Throughout the entire series, Dr. Claw is an unseen character. Only his arms and gauntleted hands are visible, leaving the viewer to guess as to his face and body. He is usually at a computer terminal where he monitors his various schemes, often in a creepy old castle. Although he is aware of Gadget's idiocy, he believes the Inspector to be his greatest enemy, never fully realizing that it is actually Penny and Brain who foil his plots in each episode (although he or his M.A.D. agents have captured Penny and sometimes Brain a number of times). Dr. Claw's preferred mode of transportation/escape is the M.A.D. Mobile, a black and red vehicle that can transform into a jet or a submarine. He is always seen with his fat pet cat M.A.D. Cat, who reaps the benefits of his brief victories and bears the brunt of his defeats. Dr. Claw's catch-phrase is "I'll get you next time, Gadget! NEXT time!" It is heard at the end of every episode, during the credits, and is followed by a loud "Meow" from M.A.D. Cat.