Male. A polar bear and the Captain of the Octonauts. He possesses immense strength, physical ability, and mental fortitude, and is the most skilled pilot of the Gup fleet. He carries an Octo-compass on his belt. He speaks with a navy-like discipline but has a heart so warm that he has never once lost his temper, even when the crew makes mistakes. Despite his bravery, he suffers from claustrophobia due to a childhood accident where he fell through an ice hole, though he partially overcame it after escaping a cenote. He is addressed as 'Captain'.

Male. A cat and the Lieutenant of the Octonauts. He is the strongest after Barnacles. Coming from a family of pirates, he often tells the crew various legends, though these stories are usually exaggerated versions of real animal traits. He is fearless and bold but has a phobia of spiders, which he overcame after meeting sea spiders. He often adds a playful lilt to his speech. He sometimes mispronounces animal names and is skilled at performing backflips. He shouts "Yeow!" when excited and his catchphrase is "Shiver me timbers!"

Male. An Adélie penguin and the Octonauts' medic. He is timid and very shy, but becomes braver than anyone when an animal is sick or injured. He is best friends with Kwazii. He is physically weak and is the smallest member after Tunip. Due to his gentle nature, he speaks more softly than the others. Although he looks like he isn't wearing anything, he actually wears a full-body suit that perfectly matches a penguin's coloration. His catchphrase when surprised is "Flappity flippers!"

Female. A dachshund who serves as the Octonauts' IT officer and photographer. She always carries her camera and treasures it dearly. She is energetic, positive, and kind. Her mechanical skills are top-tier, rivaling Tweak's; while Tweak handles development and repairs, Dashi often handles test piloting, such as with the Octo-Max Suit. She often gets into trouble while out on expeditions with Shellington. She sleeps wearing headphones.

Male. A sea otter and the Octonauts' marine biologist. He always carries a magnifying glass with incredible power—strong enough to see the cells of a coral reef. While highly knowledgeable about marine life, he can be a bit clumsy. He was originally a terrible pilot due to his lack of mechanical aptitude, but he has improved recently, though Dashi still usually takes the helm for him. Despite being a sea otter, he is allergic to sea urchins.

Female. A rabbit and the Octonauts' engineer. She loves carrots immensely—she reportedly ate a thousand carrots while building the Deep Sea Station. She wears a pink headband and often plays console games in her room. When flustered or surprised, she twists her ears like a pretzel. Her catchphrases include "Muncha, cruncha, muncha" and "Faster than a dancing dolphin." She is originally from the Florida Everglades.

Male. A Dumbo octopus, oceanographer, and the founder of the Octonauts. He has a somewhat cynical personality. While he rarely goes on field missions, he always joins the crew when the Octo-alert sounds. Despite being a Dumbo octopus (which usually can't), he is capable of shooting ink. He usually moves around the Octopod in a motorized chair. Though not tech-savvy, he once managed to clumsily perform the 'Octopod Manual Override' that usually only Barnacles can do. With eight arms, he is an unbeatable ping-pong player. He is addressed as 'Professor'.

Male. A 'Vegimal'—a creature that is half-tuna and half-turnip. He is the head cook of the Octonauts. When scared, he faints while spinning 180 degrees. His signature dishes are 'Fish Biscuits' and 'Kelp Cakes'. He is very fond of the Vegibots, which he claims are his own invention. He speaks both normal language and Vegimal (e.g., "Cheepa, cheepa!"). He has a yellow upper body, turquoise lower body, and green leaves on his head.

Exploration assistant robots stationed at the Octo Deep Sea Station. There are green (Unit 3), light blue (Unit 2), and yellow (Unit 4) models. They have video cameras in their eyes to transmit footage and pincers to lift objects like rocks. Their arms can extend, though they cannot lift extremely heavy items. Pressing the protrusion on their head toggles the system on or off. They do not speak.

A robot with a system similar to the Octobots but equipped with a cooking program. It looks similar to Tunip. Consequently, it speaks like Tunip, saying "Cheepa, cheepa," albeit with a metallic synthesized voice. It can also speak normally. Like the Octobots, its system is toggled by pressing the green protrusion on its head.