Cuttlefish

"This unreasonably attractive gentleman goes by the name of Cap'n Cuttlefish. He’s a decorated hero who fought in the Great Turf Wars of legend between the Inklings and Octarians. He now keeps solemn vigil over Octo Valley, watching for any fishy behavior. Though his clothes may be tattered, his heart is pure and nothing escapes his razor-sharp gaze. He also TOTALLY didn’t write this post."

- Live from the Squid Research Lab

Cap'n Cuttlefish (Japanese: アタリメ司令 Atarime Shirei) is a main character in Splatoon, and the only known Inkling older than 21 years old. He acts as a guide for the protagonist, issuing them the Hero Suit and title of Agent 3 in Octo Valley. He is also the grandfather of Callie and Marie.

History
Prior to the ultimate end of the Great Turf War, Cap'n Cuttlefish served as leader of a division called the Squidbeak Splatoon alongside Ammoses Shellendorf, Judd, and two unidentified Inkling soldiers. It is unknown what he did between the end of the war and the beginning of Splatoon, but he seems to have changed little.

Splatoon
Cap'n Cuttlefish can be found poking his head out of a manhole in the corner of Inkopolis Plaza. On the first time the player arrives at Cuttlefish's shack in Octo Valley, he introduces himself and recruits the player as Agent 3 to help take back the Great Zapfish from the Octarians. He provides assistance throughout the levels, until the completion of The Rampaging Octowhirl!, where he gets kidnapped by DJ Octavio. Agents 1 and 2 take over his role, until the final mission, where Agent 3 battles DJ Octavio to rescue Cap'n Cuttlefish, who is tied up in a chair. During the 4th phase, the Squid Sisters override the boss music, allowing Cuttlefish to set himself free.

Replaying the final mission results in new dialogue, describing how DJ Octavio escaped from his globe and recaptured Cap'n Cuttlefish.

Splatoon 2
In Splatoon 2, Marie takes over the role of Agent 4's guide / mentor. Sunken Scroll number 25 reveals Cap'n Cuttlefish went off travelling with Agent 3 for some kind of research trip "at the cape".

Octo Expansion
He will reappear in the Octo Expansion pack, once again providing the role as the guide to Agent 8. In the expansion, he wears a green tracksuit, and his cap is white and worn backwards. He also has square headphones around his neck.

Personality and traits
Cap'n Cuttlefish is a decorated hero who fought in the Great Turf Wars of legend between the Inklings and Octarians. He now keeps solemn vigil over Octo Valley, watching for any fishy behavior. Though his clothes may be tattered, his heart is pure and nothing escapes his razor-sharp gaze.

Cap'n Cuttlefish's favorite food is crab cakes❌/biscuits, as pointed out both by himself and Agents 1 and 2. He is often distracted by them, giving DJ Octavio the chance to escape from his snow globe prison.

Trivia

 * In the main hub of Octo Valley, the player can ink Cap'n Cuttlefish; he will eventually shake off the ink. However, it takes a considerable amount of ink to completely cover him, though, suggesting that he may be more resilient than the average Inkling, despite his age and frail appearance.
 * His cane is one of many Bamboozlers used by Inkling soldiers in the Great Turf War. However, he has never been seen to use it for its original purpose in-game, only as a cane. Interestingly, he is shown to be using it in a credits art.
 * On the corner of his shack, Cap'n Cuttlefish has taped up two small photographs of his grandchildren, one of Callie and one of Marie.
 * His shack appears to be filled books and zapfish dolls, along with pictures of octarians in the front.
 * During the initial tour of Inkopolis upon starting the game for the first time, he is referred to as a "creepy old dude".
 * The Legendary Cap is modeled after Cap'n Cuttlefish's signature hat.
 * In the Octo Expansion trailer, he is seen saying "I'll take your stunned silence as a YES!" to Agent 8. This mirrors 's "I'll take your awkward silence as a yes." to Agent 4, which in turn mirrored Cuttlefish's own "I'll take your silence to mean, 'Yes, of course I'll help!' " to Agent 3.
 * According to the first artbook, Inklings are able preserve their bodies by sun-drying, which explains Cap'n Cuttlefish's long lifespan.