Led by Captain Barnacles Bear, the Octonauts is a group of eight adventurers dedicated to explore the ocean and protect sea creatures from danger.
- Badass Crew: A group of animals who save animals from danger.
- Badass Adorable: All of them.
- Blue Is Heroic: Every member of the group wears at least one blue accessory.
- Freudian Trio: Demonstrated in the first ten seconds of the opening theme.
- Mixed Animal Species Team: The team are undersea explorers consisting of a polar bear, a cat, a dog, a penguin, a sea otter, a rabbit, an octopus, and a group of plant-animal hybrids.
- Ridiculously Cute Critter: They are all designed to be as cute as possible.
- True Companions: They all have each other's backs no matter what happens.
- Vague Age: We can assume they're at least young adults.
Captain Barnacles Bear
- Voiced by: Simon Greenall (speaking), Ross Breen (singing)
The Leader of the Octonauts. Barnacles is a polar bear who commands every mission the Octonauts perform. Being always the first to help whenever someone is in danger, he is loved by his entire crew, and he loves his crew back.
- Alliterative Name: Barnacles Bear.
- All-Loving Hero: Is as caring about sea creatures as he is serious about his work.
- Beary Friendly: Likely the nicest character on the show next to Peso. And he is so cute!.
- Blue Is Heroic: More than any other member. His entire wardrobe is blue (or at least has blue accents).
- Cute Bruiser: "Bruiser" might be a stretch, but he sure is cute.
- The Captain: No, really?
- The Good Captain: Always looking out for his teammates.
- Genius Bruiser: Barnacles is incredibly strong, but he is by no means stupid.
- Gentle Giant: Not that large, but strong is sweet natured.
- Father to His Men: When asked, he explains that he takes care of his crew.
- Fully Dressed Cartoon Animal: The only character on the show to be fully-clothed.
- Voiced by: Rob Rackstraw
Barnacles' first lieutenant. Kwazii is an impulsive cat with a mysterious pirate past. He believes in so many different kinds of sea monsters and legendary beasts that he's also considered the crew's cryptozoologist instead of just a lieutenant.
- Adventurer Archaeologist: For all that he proclaims that he's a pirate, Kwazii's interests in exploring mysterious places and locating artifacts has him much closer to one of these.
- Berserk Button: When Kwazii's around, you treat Captain Barnacles with respect. And it does not matter even if you don't know who he is.
- Captain Crash: It's not that Kwazii can't bring a craft in safely, but safety is one of the first things he overlooks when he gets overly excited. Tweak lampshades this when repairing the GUP-B at one point.
- Catchphrase: "Shiver me whiskers!"
- Cute Kitten: Not an actual kitten, but this counts.
- Eyepatch of Power: To go along with the pirate theme, as well as to emphasize his action-oriented nature, he bears one. A few times, he lifts it to reveal that it's just an affectation and that both of his eyes work fine.
- Fiery Redhead: His fur is more orange than red, but boy, is he fiery!
- Half-Dressed Cartoon Animal: Only wears a hat, eyepatch, neckpiece, and shoes.
- Hot-Blooded: Any time the prospect of action comes up, Kwazii at the bare minimum eagerly volunteers.
- Identical Grandson: Kwazii is virtually identical to his grandfather, Calico Jack. The difference is in their outfits - Calico Jack dresses like a stereotypical Pirate, while Kwazii has the collar and boots of an Octonaut, with the only pirate affectation being an eyepatch. Also, the two wear their eyepatches on different sides.
- Leeroy Jenkins: In spades. One Running Gag is that Barnacles will tell the assembled team what they need to do, and when he turns to Kwazii, he finds that Kwazii has already jumped into the water and is swimming towards the objective.
- The McCoy: To Barnacles' Kirk and Peso's Spock
- Nice Guy: Kwazii is rather short tempered, impatient and rebellious, but also one of the most easiest Octonauts to become friends with.
- Nightmare Fetishist: On the "fascination with creepy things" end of the scale.
- Number Two: To Captain Barnacles.
- Keet: Oh dear god.
- Know-Nothing Know-It-All: Kwazii is always claiming a random animal as a sea monster, and he's wrong every time.
- Pirate: He is very proud of being a pirate. However, this is also overlaps with The Pirates Who Don't Do Anything.
- Red Oni, Blue Oni: Very, very red to Barnacle's blue.
- Sensitive Guy and Manly Man: The Manly Man to Peso's Sensitive Guy.
- True Companions: Barnacles is his best friend as proven by the fact that they work together the most and their various fist bumps. The other Octonauts are equally important to them; the instant any of them are in trouble, and Kwazii is eager to rush in to help them out.
- Verbal Tic: Tends to refer to fish(es) as "fishy/fishies".
- Why Did It Have to Be Snakes?: He is afraid of spiders. Spider crabs are an exception, though.
- Voiced by: Paul Panting (UK version), Wayne Grayson (US version)
The medical officer of the Octonauts. He is a nice penguin who likes helping people. Peso is a bit shy and can be scared easily, but whenever someone needs help, he is the first to go into action.
- Alliterative Name: Peso Penguin.
- All-Loving Hero: See his second Catchphrase - he wants to make sure everyone is healthy and happy, and he works hard at it.
- Badass Pacifist: Regardless of the situation, Peso will never attempt to hurt or even hold back anyone doing anything threatening, even if he's under threat - he won't even use his absurdly fast bandaging skills to leave them Bound and Gagged. This does not stop him from stepping up to help out anyone who needs help. There's also the fact that he's extremely skilled at the various skills of penguins - he tied a professional athlete at the penguin equivalent of a triathalon.
- When surprised or alarmed: "Flappity flippers!"
- When someone needs medical attention: "I'm a medic. I help any creature who is sick or hurt, no matter what."
- Cowardly Lion: He typically will hang back in more dangerous situations, sometimes hiding behind Barnacles or Kwazii when hearing about or seeing anything dangerous. The second someone needs medical attention, though, he immediately puts all that aside and acts quickly to save whoever needs it.
- Everything's Better with Penguins: Especially medic penguins!
- Funny Foreigner: The US version has him with a heavy Spanish accent.
- The Medic: Anyone is hurt, and he's on the case immediately. In a few episodes, the drama is due to either getting the injured patient to him or getting his medical bag back to him so that he can administer treatment.
- The Heart: He always goes out of his way to help sick animals, no matter how scary they are.
- Gratuitous Spanish: In the US version, he'll occasionally use Spanish words such as "adios".
- Sensitive Guy and Manly Man: The Sensitive Guy to Kwazii's Manly Man.
- Lovable Coward: But he can be brave when he has to be.
- The Spock: To Barnacles' Kirk and Kwazii's McCoy.
- When All You Have Is a Hammer...: Apparently, the only useful item in Peso's medical bag is a nigh-infinite supply of bandages. That said, in addition to their obvious medical use, Peso has also used them to create a handy sling, swung with them like a rope, used them to build a tent to protect from weather, and much more.
Professor Inkling Octopus
- Voiced by: Keith Wickham
Professor Inkling, a Dumbo Octopus, is the founder and mentor of the Octonauts. He rarely goes on missions, but his knowledge of marine biology is an asset.
- Bookworm: He practically lives in the Octopod's library.
- Combat Tentacles: In one episode, he used a robotic suit that causes the Octopod to mimic his movements to escape an underwater tornado.
- Let's Get Dangerous!: For the most part, Inkling prefers to just act as an academic. However, the time that a colossal squid grabbed the Octopod, he donned a remote harness that allowed him to control it and revealed that he's an expert wrestler.
- Mr. Exposition: Sharing this trait with Shellington, Inkling is frequently responsible for telling Barnacles, Kwazii, and Peso important details about the sea life that they're dealing with.
- Non-Action Guy: Inkling is not particularly strong or capable of defense outside of ink clouds, so he mostly just spends time on the bridge or in the library.
Dr. Shellington Sea Otter
- Voiced by: Keith Wickham
The team's marine biologist. Shellington is always there whenever the Octonauts need information about any creature they might encounter in their adventures.
- Adorkable: He's a cute, nerdy sea otter.
- Alliterative Name: Shellington Sea Otter.
- Attention Deficit... Ooh, Shiny!; He can get easily distracted by some tings he's interested in.
- Catchphrase: "Jumpin' jellyfish!"
- Ditzy Genius: Intelligent, but he can't drive a GUP and gets easily distracted by animals he finds interesting.
- Drives Like Crazy: Cannot drive a GUP very well.
- Dub Name Change: Downplayed. In the original UK version, he's often referred to as Dr. Shellington. The US version drops the "Dr." part of his name.
- Dr. Exposition: Sharing this trait with Inkling, Shellington is frequently responsible for telling Barnacles, Kwazii, and Peso important details about the sea life that they're dealing with.
- Playful Otter: He's playful with the Vegimals.
- Repeating so the Audience Can Hear Tunip's Simlish.
- The Smart Guy: When the Octonauts need information for any kind of creature, he is the go-to guy.
- The Klutz: That's why he is rarely seen driving a GUP.
- Translator Buddy: To Tunip and the other vegimals.
- Voice with an Internet Connection: In most episodes, Shellington stays in his lab and relays information about the sea life that others (usually Barnacles, Kwazii, and/or Peso) are encountering outside the Octopod via the radio.
- Voiced by: Jo Wyatt, Jaimie Kelton (US version, season 1 only)
Tweak is the team's engineer, dedicated to work on special devices to help the Octonauts in their missions or maintain the Octonauts. She is very fond of eating carrots.
- Amazing Technicolor Wildlife: A green rabbit.
- Catchphrase "Faster than you can say 'Buncha munchy crunchy carrots!'"
- The Engineer: She doesn't just design all of the machinery the Octonauts use, but she's also the one who builds and maintains it all, as well.
- Girly Girl And Tomboy: Tweak is the Wrench Wench tomboy to Dashi's Communications Officer Girly Girl.
- Punny Name: Her name is Tweak, and she's a mechanic. Let that sink in.
- The Smart Girl: Knows a whole lot about tech, GUPs, or just anything to do with building.
- Southern-Fried Genius: The genius part (being both the designer and builder of all the GUPs) is established from the beginning, and the fourth season reveals that she's originally from the Everglades in Florida.
- Stock Animal Diet: As already mentioned, she is very fond of her carrots.
- Voiced by: Teresa Gallagher (UK version), Mary Murphy (US version)
The Octonauts' information officer. Dashi is entrusted with maintaining and controlling the Octopod's computers. She also provides information to the Octonauts in the field. Dashi is a very good photographer and has a collection of cameras and pictures.
- Adaptation Name Change: In the original books, she was named Sauci.
- Alliterative Name: Dashi Dachshund (UK), Dashi Dog (US).
- Communications Officer: In contrast with Tweak, Dashi is the expert at software and radio communications, and she's frequently shown to be coordinating their radios.
- Damsel out of Distress:
- While waiting to be rescued from a whale shark's stomach, passes the time by taking interesting photos. No distress here.
- Calls for help... lifting a large creature back into the river where it belongs.
- Dub Name Change: The US version changes her surname to Dog.
- Girly Girl And Tomboy: The pink-skirted Girly Girl to Tweak's shorttank tomboy.
- Intrepid Reporter: Just watch her report the Iron Clam Competition.
Tunip the Vegimal
- Voiced by: Michael C. Murphy
Tunip is half-vegetable, half-animal creature that serves as the Octopod's cook and gardener. He and his fellow Vegimals are usually seen working to prepare meals for the Octonauts.
- Badass Adorable: He used to be just The Cutie, but became a badass in "The Very Vegimal Christmas".
- Catchphrase: "Cheepa Cheepa!" when excited.
- Daddy's Boy: Shellington loves all his fellow Vegimals, but is particularly close to Tunip.
- Fainting: You know that something bad happens whenever Tunip faints.
- Genius Ditz: Him and most of the other vegimals are kinda ditzy at times, but they are excellent chefs. Plus in "The Very Vegimal Christmas" he and the Vegimals invented a new GUP.
- Intelligible Unintelligible: Shellington understands him.
- Planimal: Like all Vegimals.
- Speaking Simlish: It's vaguely similar to English (such that there's usually a word or two that can be picked out and the meaning can be gleaned even when Shellington is absent), but most of Tunip's dialogue (along with the other Vegimals) is just random babble.
- Supreme Chef: His fish biscuits are apparently the best food in the entire ocean to the extent that, regardless of their usual diet, any sea creature that eats them finds them irresistible. The only exception to this were the lionfish, and even then the problem was just that they had been eating them for days.
- Took a Level in Badass: In "The Very Vegimal Christmas", Tunip and the Vegimals build a new GUP and use it to save the Octonauts from danger.
- The Unintelligible: To anyone who isn't Shellington.