It is rumored that Don Adams left the series about 65 episodes into the series, and that the voice of Inspector Gadget in Season 2 was a Don Adams impersonator.
Don Adams based Gadget's voice on his previous role as Maxwell Smart.
The character voices for the show were recorded in Toronto, Canada; however, the original script was written in France, and the animation was done almost entirely in Japan.
In some episodes, Penny is seen watching Heathcliff, another cartoon produced by DiC Entertainment. Additionally, in one episode, Gadget drives his car through a junkyard, and some of the cats from Heathcliff can be seen in the foreground. And in "The Incredible Shrinking Gadget," we see that one of Penny's dolls is Riff Raff, one of the cats from the show.
One of the MAD Agents--the tall, thin, stupid one with the high-pitched voice--was patterned after the character Lenny in "Of Mice and Men" (the role played by Lon Chaney Jr).
Jesse White and Gary Owens were both considered for the role of Gadget. In fact, Owens originated the inspector's signature "Wowsers!" However, Don Adams was given the part because his reading of Gadget's lines was considered the best.
Two versions of the pilot episode exist. The earlier version features completely different opening and ending/credits sequences.
This is the only episode in which Gadget has a mustache.
For the pilot episode only, Penny was voiced by Mona Marshall. In the rest of the first season, Cree Summer did the voice work; in the second season, she was replaced by Holly Berger.
John Stephenson (Mr. Slate on The Flintstones, and countless other Hanna-Barbera cartoons) voiced Chief Quimby in the first episode. Stephenson also did the voice of a few policemen and numerous announcers.
The MAD agent who carries a stick of dynamite as the Olympic torch, though never seen in any more episodes, became the model for one of the Galoob-made Inspector Gadget toys. Also, a plastic Inspector Gadget lunchbox from the '80s depicts one of the scenes from this episode.
During the scene where a bird pops Gadget's inflated Gadget Coat, there is a brief animation goof: Only Gadget's head and hands are drawn into the scene, leaving him bodiless for a few frames.
Trivia: Individual Episodes
In the episode "Funny Money," which takes place in an insane asylum, the inmates were modeled after the show's animators.
In the beginning of the episode "The Invasion," Gadget, Penny, and Brain are watching a movie in which a robotic gorilla is destroying buildings. This is actually an archived scene from the first episode, "Gadget in Winterland."
In the episode "Gadget at the Circus," a minor goof-up in the ink-&-paint department turns MAD Cat's nose black for a few frames.
In the episode "Art Heist," during the safety tip at the end of the episode, Gadget walks down the street with Penny and Brain. One of the places they pass is a clothing store, which has a window display featuring two strange signs reading "Baung Baung" and "New Wave." Signs in the background that have meaningless or indecipherable lettering are common to the series, as much of the animation was done in Japan.
In the episode "Greenfinger," there is a slip-up in Penny's dialogue. At one point she refers to "The Greenfinger Institute" as "The Greenfield Institute."
In the episode "The Japanese Connection," Claw travels to Japan to form an alliance with the criminal Waruda-San. Although Waruda-San's Siamese cat is never referred to by name in the episode, its official name (in the storyboards and character design animations) is Syco.
In the episode "Pirate Island," there is an animation error. In one scene, one of the billionaires yells, "Threaten us some more! Ha ha ha!" but the MAD Captain's mouth moves instead of the billionaire's. Also in the episode, listen for Don Francks (as the MAD Captain) adding a little personality to his character by attempting a Frank Nelson impression.
In the episode "Luck of the Irish," when Gadget climbs a tree to get Penny's kite down for her, he calls out "Don't worry Penny, I got it!", but his lips don't move.
Also in "Luck of the Irish," listen closely to the crowd in the pub scene. Someone shouts "Gimme a beer!"
In the episode "The Emerald Duck," notice the nod to Don Adams' previous show, Get Smart. At the beginning of the episode he comments on "the second biggest duck I've ever seen," a variation on one of his catch-phrases from Get Smart.
Also in "The Emerald Duck," there is a contradiction between script and animation. While in a boat with Penny, Gadget says, "I'm taking this duck caller back to the store -- it doesn't work!" and proceeds to toss it into the water.
In the episode "Fang the Wonderdog," the name of the dog is likely a throwback to Get Smart. In a few episodes, Maxwell Smart/Agent 86 worked with a canine agent named Fang.
In the episode "Gadget's Clean Sweep," Gadget travels back in time. He brings Penny to a seedy part of 19th-century London and immediately leaves her alone on the docks so he can hit the bars!