*Penny is Inspector Gadget's niece and one of the main protagonists of the franchise. Penny secretly helps out her Uncle Gadget with his missions and does all the work, but she lets him get all the credit in the end.

Penny secretly does all the work during Inspector Gadget's missions, despite him always taking all the credit afterwards. She usually uses her computer book and video watch to help her solve the cases. It is not stated where Penny got them or why she has them in the first place, but given Penny's super intelligence, she probably built it herself.

Penny is ten years old in the original series, with later depictions happening after two-year timeskips.

Penny is precocious, intelligent, brave, cute, tomboyish, resourceful, and anonymously solves the cases for her Uncle Gadget, something which he is totally oblivious to. Penny also loves her uncle very much and looks up to him. While it is not stated if she and/or Gadget have any other family members in the TV series, movies, or spin-offs, Gadget seems to be the only family she has got, and "Gadget and Old Lace" and a few episodes of Gadget and the Gadgetinis, including "No Brainer", confirm her to be an orphan. Penny foils Dr. Claw's plans, leaving Gadget to get all of the credit for doing so, even though he didn't do anything at all. This makes sense because Penny would be in serious danger if she got the credit.

Penny often stares around M.A.D.'s hideout or setup location to find out what they are up to; however, she usually ends up getting caught by Claw's henchmen and she either escapes by herself or calls her loyal pet dog Brain to rescue her. But when she and Brain are both captured, Gadget becomes exceptionally useful and competent and goes out to rescue both of them. Gadget loves Penny more than anything and he sees acting like a pretty girl. Penny is also very knowledgeable; for example, in "Clear Case", when she and Brain are in a laboratory of a diamond mine in South Africa, she knows how M.A.D agents are making invisibility suits to scare off miners by making them think they are ghosts. Quoting: "Diamonds refract light. They discovered a way to grind them into a powder and make a diamond cloth. It's like a coat made of mirrors: It deflects light so you can't see it."

Penny is also very patient and progressive, particularly when putting up with her uncle's clumsiness and stupidity.

Penny has shoulder-length blonde hair styled in pigtails. Penny's age throughout the original animated series is 10 years old.

In the original cartoon, Penny wears a red short-sleeved T-shirt with a thick white stripe in the center, olive green pants with light green knee pockets, alongside red and pink sneakers. In season 2, she typically also wears one of the following: a blue and white sports jacket, a red jacket with black and pink trim, a pink sports jacket, or a khaki vest. She was seen in a bikini three times, two of them red and the last is blue. The safety tip in "The Boat" depicts her wearing much more conservative swimwear, consisting of the T-shirt paired with olive green beach shorts. Her usual sleepwear is a light blue nightgown, though she is occasionally seen wearing two-piece pajamas of the same color.*