Accidental Hero: Believe it or not, there are actually a number of times when Gadget is legitimately helpful and actually contributes towards solving the case. It's just that he tends to do it purely by accident.
Repeated line whenever Gadget is congratulated for solving the case: I did?
Actor Allusion: "Would you believe I was practicing my swan dive?"
Adults Are Useless: However, when Gadget knows Penny is in danger, he becomes scarily competent.
Fearless Infant: Gadget was shown to be one in a flashback of the final episode, where he is seen as a baby witnessing crime boss Spuds Malone gun down people with his potato gun the Red Rose and being completely unfazed by the chaos.
Flanderization: In the pilot, Gadget was bumbling, but not nearly as oblivious and managed to fend off most of MAD's schemes via competance. Early episodes occasionally flip flopped between this depiction and his iconic Accidental Hero persona before finally settling for the later. This was taken Up to Eleven where most spin offs such as Gadget And The Gadgetinis are concerned.
Flipping the Bird: Surprisingly in a children's series, he does this in the OPENING sequence! Granted, he wasn't trying to be deliberately offensive; his bird just happened to be a flashlight.
Horrible Judge of Character: Gadget always believes the lies MAD agents tell him. He'll even trust MAD agents that aren't even bothering with deceiving him and are just trying to kill him ("Ah! The welcoming commitee!"). This goes all the way to the opposite end of the spectrum. He'll spot Brain in disguise, and instead of recognizing Brain, he'll think Brain is the MAD agent!
Let's Get Dangerous: Very, very rarely, Gadget showed competence and was able to avert disaster all on his own. This tends to happen when Penny is in danger.
The Other Darrin: Fake Brit Gadget from the pilot was voiced by Gary Owens in the first draft. A revision had him voiced by Jesse White using an impersonation of Don Adams. Finally, Don Adams himself played the role in the third and final version of the pilot.
Maurice LaMarche played Gadget in Gadget And The Gadgetinis and the animated direct-to-video films Inspector Gadget's Last Case and Inspector Gadget's Biggest Caper Ever.
Papa Wolf: When he knows Penny is in danger, Gadget becomes virtually unrecognizable (and unstoppable) as he becomes the superhero he is supposed to be. For what it's worth, one of his few talents seem to be as a guardian, when not oblivious to some villain on her tail, he raises Penny rather well and gives rather intelligent life lessons.
This also extends to other people Gadget cares about. He's gone to similar lengths to save Brain (when he actually knows that he's dealing with Brain, as opposed to thinking the disguised Brain is a MAD agent) and Professor Von Slickenstein, the scientist who gave him his gadgets.
Parental Obliviousness: Gadget has no idea that it's his niece solving his cases and saving the world.
Berserk Button: Just seeing Gadget, or even simply having to mention his name, can make Dr. Claw angry enough to smash holes in his desk or shatter diamonds with his bare hands.
Catch Phrase: "I'll get you next time, Gadget! Next time!"
Corrupt Corporate Executive: For the movie. Also any episode that revolved around MAD setting up a legitimate business and then wiping out their competition by some underhanded means, leaving Dr. Claw with a monopoly.
Exact Words: From the episode "The Invasion": "I said I feel like singing!"
The Faceless: Not only faceless, but also bodiless as only his hands and arms are ever shown to the viewers. Luckily, in the movie, his whole appearance is RupertEverett.
Karma Houdini: Usually played straight in that he always avoided getting arrested, but some episodes subvert it and have Claw suffer a minor problem as he makes his getaway, such as being trapped at the bottom of the arctic waters in "Gone Went the Wind", getting frozen in "The Quimby Exchange", and getting hit by the blast of the Red Rose potato gun in the final episode "Gadget and the Red Rose".
Brian Drummond provided Dr. Claw's voice in Gadget And The Gadgetinis and the DTV movies Inspector Gadget's Last Case and Inspector Gadget's Biggest Caper Ever.
Slouch of Villainy: Throughout the series, he only watches the events from his lair or car.
Surrounded by Idiots: Even with Penny always screwing up his plans, you sometimes think he might be ruling the world by now if his henchmen weren't all so stupid.
Villain Exit Stage Left: Whenever he's actually at the scene of a MAD activity, he'll typically escape in the MAD Mobile once the Gadget family ruins his scheme.
Nice Girl/Friend to All Living Things: Penny rarely shows anger, hardly ever even gets annoyed (even with her uncle's antics), and the number of people she shows intense dislike for throughout the entire franchise can be easily counted on one hand. As a result, she has a knack for making friends and allies at the drop of a hat.
Non-Standard Character Design: In comparison to the other very cartoony designs in the show, Penny's is noticably more anime inspired and realistically proportioned. Gadget And The Gadgetinis gives her a somewhat wackier design, though still slightly more subtle than the rest of the cast.
Not so Above It All: She may be the most competent and mature person in her household, but mention her favorite singer and she still goes into shrieking fangirl mode.
Only One Name: Penny was never given a last name, though a lot of people just assume it's Gadget.
The Other Darrin: In the pilot she was voiced by Mona Marshall. In the second season, Holly Berger took over the role from Cree Summer.
Parental Abandonment: It's confirmed in the second season that Penny's parents are apparently deceased. We only have Dr. Claw's word for it but according to him, Penny is Gadget's only living relative.
Action Pet: Although more wacky than outright action, he still goes through things that one would have to be tough to get though.
Beleaguered Assistant: Occasionally averted when Gadget actually saves Brain. This usually happens when Gadget thinks he's a MAD agent and is trying to capture him, and ends up grabbing Brain right before he'd fall to his death.
My Instincts Are Showing: Though usually a neurotic Straight Man with more human intelligence than most of the police force combined, Brain sometimes has displays of puppy-like friskiness. For example, at one point when Gadget tries to throw away some explosives, he mistakes it for a stick and excitedly plays fetch with it.
The Other Darrin: Dan Hennessey voiced him in the first season. The second season had Maurice LaMarche take up the role.
Something Only They Would Say: Apparently, only the real Gadget would malfunction without warning and injure him with his gadgets. Quimby uses that fact to Spot The Impostor in one episode.
