Male. The Captain of the Octonauts, yet gentle and kind. He suffers from claustrophobia due to a childhood accident. He is a warm and dependable polar bear. He is a skilled driver and loves vanilla pudding. He is very strong but only uses his strength when absolutely necessary.

Female. The representative of the creator's OCs (Banmil, Dian). She doesn't act like a leader; she's more like a chaotic kid and a gag character. However, she can be serious when the situation calls for it. She loves eating, especially pudding. She is strong, has great physical stats, and is incredibly energetic and kind. She is a human.

Male. The Lieutenant of the Octonauts. He loves exploring and is cheerful and lively. Though a former pirate, he is a dedicated Octonaut. When surprised, he says "Shiver me timbers!" and when excited, he shouts "Yeow!" He can be stubborn but is a kind cat. He is deathly afraid of spiders and loves sea-grass cakes.

Female. Her real name is Milky, but she is called Banmil (short for 'Reverse Milky') to distinguish them. She looks delicate and speaks in a kind, beautiful manner. She uses polite speech with everyone. She is kind, incredibly strong, and has good physical stats. She occasionally keeps Milky in check when she goes overboard. She is a human.

Male. An adorable penguin. He is the medic; though timid and lacking courage, he becomes brave for his patients. He is extremely kind and, like Kwazii, says "Flapping flippers!" when surprised. He likes peppermint-flavored kelp cakes. He is easily frightened and is notably short among the Octonauts (except for Tunip). He waddles because of his short legs.

Female. She never eats seafood or fish; if offered any, she will demand to know what she did wrong to deserve such treatment. She shows little emotion and carries a fish around because she likes them. She is always in a diving suit. She is very shy and hard to get close to, but she is kind. She is a human.

Male. A marine biologist who is ironically allergic to sea urchins. He seems a bit afraid of heights and is very easygoing. He feels like he's missing about 2% of his focus sometimes. He is a kind sea otter. He was the one who first discovered Tunip. Only Shellington can understand what Tunip says.

Male. An adorable Vegimal (part vegetable, part animal) who speaks a unique language (though he occasionally speaks Korean). He calls Shellington "Shelly-ton" and uses the word "Cheepa" for joy, sadness, excitement, or just about anything. He is a cross between a turnip and a tuna. He is the cook and is very skilled at it. His actions are as cute as his face. When shocked, he does a 180-degree turn and faints. He waddles like Peso due to his short legs.

Female. The engineer. She loves carrots and is a genius with machinery. When a machine breaks, she says, "Don't worry, I can fix this in a jiffy with my crunchy carrot power!" She can sense immediately if even one of the Gup vessels she built has a problem. She loves gaming so much she stays up all night playing. When surprised, she twists her ears like a pretzel. She is a rabbit.

Female. She loves taking photos. Her role involves managing communications and information security. She is lively and full of energy. Her hobby is surfing, and she is very curious.