The wonderfully wacky characters of Ready Jet Go! have so much depth, that we had to make a separate page just to analyze them all. Really, the only characters without foils can be counted on 1 1/5 hands: Beep, Boop, Moonbeam, Eggplant, Dr. Skelley, and Ellen Ochoa. Beep and Boop are the exact same except for where they live; Moonbeam is just Sunspot but blue; Eggplant didn’t get to develop properly; Dr. Skelley doesn’t really have an opposite; and Ellen Ochoa only appeared once (unless you count her cameo in "Moon Face"). You're welcome.
- Mitchell and Lillian. They are both friends of Mindy, and two of the most popular recurring characters. However, they are different in many ways. Lillian is gentle, innocent, easily excitable, and a bit air-headed. Mitchell is easily pissed off, prideful, anti-social, and smart for his age. Furthermore, Lillian is an Agent Mulder who is purely good, while Mitchell is a firm Agent Scully who hides his good traits. Despite this, the very little amount of interaction they had in "That's One Gigantic Pumpkin, Jet Propulsion!" seems to prove that they are on somewhat good terms with each other. Justified as Lillian is best friends with Mindy, while Mitchell seems to like her a bit, which means that they are going to end up hanging out.
- Sean and Sydney. They are both friends of Jet and they are both his minders and kids that love science. Sean likes science facts and sometimes doesn't understand imagination being used in science. He is also more prone to panicking under pressure and, of the main characters, is the most prone to grab the Jerkass Ball (most noticeable in "Sounds Abound"). On the other hand, Sydney prefers science-fiction and using her imagination in science. She is quite calm and laid-back and is also a motherly Nice Girl.
- Dr. Rafferty and Dr. Bergs. They are both DSA scientists who are friendly and teach the kids various things about science. Dr. Rafferty is competent and is almost never used for jokes, while Dr. Bergs is a bit of a bumbling Big Eater who is often used for jokes, especially if it involves his coffee obsession. On the flip side though, Dr. Bergs has Hidden Depths - being related to Lone Star himself, while Dr. Rafferty has no depths to speak of. While there is her apparent All of the Other Reindeer childhood where she "felt like an alien", it is only implied and has never been mentioned since then.
- Mitchell and Sean. They are both the intelligent, dorky, level-headed, voice of reason within their respective groups, and they both have Youthful Freckles. They also both happen to be the love interests of their leaders (Mitchell for Mindy, and Sean for Jet). However, Sean is friendlier and more open, while Mitchell tries to shut himself out from everyone else. While Sean's desire for logic contrasts with Jet's fantastical nature, he has always liked Jet. It took a while for Mitchell to start warming up to Mindy.
- Mitchell and Sydney. They both are the only kids of their respective genders in their age groups (Sydney is the only girl in the older kids and Mitchell is the only boy in the younger kids). They also both have emerald-green eyes. However, they cancel each other out. Sydney is highly imaginative, while Mitchell claims to have a terrible imagination. Sydney is very compassionate and makes friends easily, as opposed to Mitchell, who tends to be callous and has No Social Skills.
- Lillian and Sydney. Both are the very kind-hearted and imaginative girls in their respective groups. But while Sydney is smarter and, while imaginative, knows how to separate fiction from fact, Lillian is more air headed and easily believes in the supernatural.
- Mr. Peterson and Carrot. Both are somewhat goofy fathers. Carrot embraces his silliness and is usually a nice dad, but isn't above being stern to Jet (like in "Chore Day"). Mr. Peterson, on the other hand, treats the most minor of things as Serious Business (such as mini-golf and the communications satellite not working) and almost always lets Mitchell get away with stuff.
- Jet and Mindy. Both are the enthusiastic, curious leaders of their respective age groups (Jet for the older kids, and Mindy for the younger kids). Jet is an alien who is the new kid in town, so he is rather naive about how Earth works, in contrast to Mindy, who is a young child but has a rather solid grasp on Earth culture and traditions, most of the time anyway. Another difference lies in their knowledge of space. Jet, being a space alien and having traveling parents, knows a lot about outer space and is always eager to learn more. Mindy often gets things wrong about space, like that the Sun orbits around the Earth and that there are multiple different moons orbiting Earth. Finally, their kindness. Jet is an All-Loving Hero who has astounding patience with jerks like Mitchell and Zerk, and always owns up to his mistakes. Mindy is nice most of the time, but she is rather self-centered, sassy, and sarcastic, doesn't like to admit her mistakes, and is often rude to Sean.
- Celery and Zucchini. They are siblings who live on different planets (Earth for Celery, and Bortron 7 for Zucchini). They are both cheerful and benevolent. Celery has a job as an intergalactic travel writer and has knowledge about outer space to spare. Zucchini has a job as a mere garbageman and is shown to be very foolish and ignorant about space and even basic Earth science (in his debut episode, he thought that Saturn's moon Titan was Earth, and in "Uncle Zucchini Babysits", he didn't know about the three states of matter).
- Jet and his cousin Zerk. Both are young Bortronian children bubbling with energy and a thirst for knowledge. Jet lives on Earth, and while he is peppy and energetic, he knows how to be calm. He is also very humble and doesn't care about being the winner. Finally, Jet is very open-minded and tolerant of other's differences. On the other hand, Zerk is hyperactive almost all the time and is never shown being calm or quiet. Zerk is a huge braggart and likes to be the best at everything he does. Finally, Zerk was outright racist to the humans in "Whole Lotta Shakin'", saying that they don't build very well.
- Face 9000 and Face 9001. Even though Face 9001 only appeared in one episode, he's fleshed out enough that one can analyze the differences between him and his brother. Both are talking Bortronian computers who are very intelligent. They also both love attention. While Face 9000 can be an Attention Whore sometimes, he is more often than not a very friendly and helpful computer. By contrast, Face 9001 is an Attention Whore pretty much all the time, on top of having a huge ego and being a jerk to his brother.
- Jet 2 and Sydney 2. They both are robot clones of two of the kids (Jet and Sydney obviously). Their origins differ. Jet invented Jet 2 for an admittedly selfish reason, so he could be at two places at once. Sydney invented Sydney 2 just so Jet 2 could have a playmate. Jet 2 also appeared way more often than Sydney 2, as he was introduced way before her.
- Sunspot and Cody, Mitchell's dog. Both are pets who reside in Boxwood Terrace. Sunspot is a Bortronian pet who is smarter than he appears and has many hidden talents, like making sound effects and pulling objects out of Hammerspace. Sunspot is also more than happy to help Jet and his friends. Ironically, despite all his incredible feats, Sunspot struggles with ordinary Earth pet things like playing fetch. Cody is an ordinary Earth dog who likes sleeping, eating, and isn't all too enthusiastic about helping Mitchell with his detective cases. Cody can do the typical things your average Earth dog can do, but only if he's offered a treat as a reward, as we learn in "Pet Sounds".
- Stella from Ready Jet Go! Space Camp is a foil to Zerk. Both are atypical Bortronian children, and both have a relationship to Jet in some way (Zerk is Jet's cousin, and Stella finds out about Jet when he becomes the number one Great Galacto fan). However, while Zerk displays Fantastic Racism towards the Earthies at first, he grows to love Earth, and isn't intentionally rude. Stella doesn't display Fantastic Racism towards Earth or Earthies, but she displays other forms of discrimination such as ageism and heightism. She is also intentionally rude towards others, though she grows out of it.
- The Great Galacto is a foil to Commander Cressida. Both are space heroes with alliterative names idolized by the main characters. However, Commander Cressida is a fictional character in a Show Within a Show, while the Great Galacto is a real person and TV show host. Commander Cressida's comics are educational in some capacity, while the Great Galacto's videos just seem to show him doing heroic stuff. Commander Cressida always has her squad with her, while the Great Galacto is a solo act - though he admits that he has a crew that helps him with his videos.
