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

A female human and 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 meme character. However, she is serious when she needs to be. She loves eating, especially pudding. She is strong, has great physical stats, is incredibly active, and kind.

A male cat and the Lieutenant of the Octonauts. He loves exploring and is cheerful and energetic. Though a former pirate, he is a loyal 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.

A female human. Her name is also Milky, but she is called Banmil (short for 'Reverse Milky') to distinguish them. She looks delicate and speaks very kindly and politely to everyone. She is nice but incredibly strong with good physical stats. She occasionally keeps Milky in check when she goes overboard.

A male penguin and an adorable medic. He is timid and lacks courage, but finds it when treating patients. He is extremely kind and, like Kwazii, says "Shiver me timbers!" when surprised. He likes peppermint-flavored kelp cakes. He is very fearful and is notably short among the Octonauts (except for Tunip). He waddles because of his short legs.

A female human who never eats seafood or fish; if offered, she will demand to know what she did wrong to deserve it. 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 timid, making it hard to get close to her, but she is kind.

A male sea otter and a marine biologist, though he has a sea urchin allergy. He seems a bit afraid of heights and is very easygoing. He feels like he's missing about 2% of his wits sometimes. He is a kind otter who was the first to discover Tunip. Only Shellington can understand what Tunip says.

A male Vegimal (part vegetable, part animal) who is incredibly cute. He speaks a special language (though he occasionally speaks Korean). He calls Shellington 'Shelly-ton' and uses the word 'Cheepa' for everything—when he's happy, sad, or excited. He is a turnip-tuna hybrid. He is the cook, very skilled at it, and 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.

A female rabbit and 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 munchy carrot power!" She can sense immediately if even one of her inventions (the Gup fleet) has a problem. She loves gaming so much she stays up all night playing. When surprised, she twists her ears like a pretzel.

A female who loves every man she sees. She is obsessed with men and acts flirtatious, while being sarcastic, dismissive, and abusive toward women. She fakes crying, but no one believes her. She flirts constantly and exhausts everyone around her.