A male polar bear and the Captain of the Octonauts. He is warm and kind. He 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 (Ban-mil, 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 a great physique, is incredibly active, and kind.

A male cat who loves exploration and is very cheerful and lively. He is a former pirate but now an Octonaut. When surprised, he says "Shiver me timbers!" and when excited, he says "Yeow!" He can be stubborn, but he's a kind cat. He is deathly afraid of spiders.

A female human. Her name is Milky, but she is called Ban-mil (short for Reverse Milky) to distinguish them. She looks delicate and speaks very kindly and beautifully. She uses polite language with everyone. She is kind, incredibly strong, and has a good physique. She occasionally keeps Milky in check when she goes overboard.

A male penguin who is incredibly cute. He is the medic; though he is timid and lacks courage, he becomes brave for his patients. He is very kind and, like Kwazii, says "Flappity flippers!" when surprised. He likes peppermint seaweed cake. He is easily scared 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 given any, she will demand to know what she did wrong. 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, yet 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 and was the one who first discovered 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" when he's happy, sad, or excited (like a catchphrase). He is part turnip, part tuna. He is the cook and is very talented at it; his actions are as cute as his face. When surprised, he faints while spinning 180 degrees. 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 the GUPs she built has a problem. She loves gaming so much she stays up all night playing. When surprised, her ears twist like a pretzel.

A female who loves every man she sees. She is boy-crazy and acts flirtatiously, while being sarcastic, ignoring, or even hitting other women. She fakes crying, but no one believes her. She flirts constantly and exhausts everyone around her.