Inspector Gadget is the main protagonist and titular character of the franchise. Gadget is a cyborg (part man, part machine) with thousands of high-tech gadgets installed in his body. Gadget is very powerful and loyal to his career as a lawman, but he is also very dim-witted, clueless, incompetent, oblivious, and gullible, but also lovable, caring, and protective. His attire and personality resemble those of Maxwell Smart (also voiced by Don Adams) from the Get Smart TV show.
While Penny and Brain secretly do all the real detective work, Gadget has a knack of inadvertently saving the day, usually without realizing he is doing so. Gadget loves his family more than anything and would do anything to keep them from harm, especially Penny. He was voiced by Don Adams in the original series and Inspector Gadget's Field Trip until Adams' retirement from voicing Gadget in 1999, Gary Owens and later Jesse White in the original series' pilot episode, and Maurice LaMarche in the Super Mario Bros. Super Show, Gadget and the Gadgetinis, the direct-to-video animated films, and various DIC Kids Network bumpers. For the 2015 series, the voice of Gadget is provided by Ivan Sherry. It is revealed in the first live action film that Gadget's real name is Jonathan "John" Brown. He is portrayed by Matthew Broderick in the first film and French Stewart in the sequel.
- His fashion sense resembles that of Inspector Clouseau from the Pink Panther cartoons. Also, in the pilot episode, Gadget had a mustache that was similar in appearance to Clouseau's. This was soon removed to avoid being sued by MGM.
- Inspector Gadget's mannerisms also appear to draw on the character of Maxwell Smart, portrayed by Don Adams in Get Smart.
- In the live-action film, Gadget worked in Riverton, Ohio as a security guard named John Brown who tried unsuccessfully on a few occasions to apply to the police academy. It was only after getting critically injured at the hands of Claw and converted into a cyborg that he was admitted into the police force.
- Gadget almost always wears the same trench coat, gloves, and hat at all times. But on very rare occasions, he has been shown to wear other outfits on his leisure time.
- In the cartoon, Gadget's real name was never revealed, but it was strongly implied that his real last name was Gadget. In the live-action film, his real name was John Brown.
- In the original cartoon, he was given his gadgets by Professor Von Slickstein. In the live-action film, it was Brenda Bradford. In Gadget Boy & Heather (which was believed by many to be about Gadget as a child), Gadget was converted to a cyborg by Myron Dabble. On a trading card, he is revealed to have had his accident from slipping on a banana peel. Other than that, his origins were never revealed.
- His, Penny Brown, and Brain's appearances in the Stephen Squirrelsky and Friends' movie spoof travels are Simba (Shrek), The Great Hedgehog Detective, The Sword in the Stone, Vanellope Von Schweetz, The Train and the Boat, Toon Age, Hoodwinked!, The Rescuers, Nikki's Adventures of Sing Along Songs Episode 4, The Rescuers Down Under, The Secret of NIMH, Nikki's Adventures of Sing Along Songs Episode 6, Skunkules, Home on the Range, Kermit's Winter Wonderland, The Little Jungle Boy, Kermiladdin 2: The Return of McLeach, AiAi the Monkey and A Day for George, The Reindeer and the Deer, Animal Story 2, AiAi the Monkey's Grand Adventure: The Search for Tails, A Cartoon Character's Life, Nikki's Adventures of Sing Along Songs Episode 7, Here Comes Winnie the Pooh, Animals, Inc, Simba 2, Miss Bianca and the Bernard 2: Fievel's Adventure, FernGully: The Last Rainforest, A Pooh in Central Park, Bubblesrella 2: Dreams Come True, The Brave Little Piglet, Kung Fu Owen, Nikki's Adventures of Sing Along Songs Episode 8, The Thomas O'Malley Movie, Kermit Returns, Fievel the Red Nosed Mouse and The Island of Misfits, Nikki's Adventures of Sing Along Songs Episode 9, Cloudy with a Chance of Meatballs, Finding Alvin, Animated Tale, The Forest Book 2, Nikki's Adventures of Sing Along Songs Episode 10, Madagascar, and Sleeping Beauty and will even be in more movie spoof travels.