Cap'n Cuttlefish - Captain Craig Cuttlefish was the leader of the Squidbeak Splatoon. He wore the original Cap of Legend, along with a button-down shirt, khaki pants, a belt, and boots. His shirt was adorned with three medals of unknown value.
Ammoses Shellendorf - A horseshoe crab who excelled in designing weapons and likely designed the original Bamboozler used during the Great Turf War. He is also the grandfather of Sheldon, who currently manages Ammo Knights.
Judd - A feline member of the Squidbeak Splatoon who presumably joined after he was awakened from his cryogenic slumber. His exact function in the platoon remains unknown, as he does not appear to be able to manage a weapon. Judd currently judges matches of Turf War and Ranked Battle and can often be seen sleeping on a pillow in Inkopolis. In Splatoon 2, he can be seen alongside Li'l Judd.
Male Inkling - This Squidbeak Splatoon member's identity is unknown. He can be seen in Sunken Scroll 15 wearing an ink tank on his back.
Female Inkling - This Squidbeak Splatoon member's identity is unknown. She can be seen in Sunken Scroll 15 leaning against a rock.
Agent 1 - One of the Squid Sisters in disguise, Callie wears a pink beanie decorated with a large golden star, a pink sweatshirt, and sunglasses to conceal her identity. As the cousin of Agent 2, the two took over Cap'n Cuttlefish's role as mentor for Agent 3 when he was captured. In the final boss battle of Splatoon, they hijacked DJ Octavio's transmission and played the Calamari Inkantation, allowing Cap'n Cuttlefish to escape his imprisonment. Agent 1 is never directly seen in Octo Valley; she is only acknowledged through Cap'n Cuttlefish's monologues and DJ Octavio's radio transmissions. In Splatoon 2, she is kidnapped and mind-controlled with "hypnoshades" by DJ Octavio, assisting him during the final boss battle before being rescued by Marie and Agent 4. She continues to support the New Squidbeak Splatoon in Splatoon 3.
Agent 2 - The other Squid Sister, Marie wears a green hat embroidered with an orange emblem, a green shirt, and a surgical mask to conceal her identity and worked with Agent 1 to stop DJ Octavio in Splatoon. Like her cousin, Agent 2 is never directly seen in Octo Valley. In Splatoon 2, she recruits Agent 4 and acts as their mentor, also appearing during the final boss battle to free Agent 1 from the mind-control of the "hypnoshades" by shooting them off with a Hero Charger. She continues to support the New Squidbeak Splatoon in Splatoon 3.
Agent 3 - The player character in Splatoon enters Octo Valley to be immediately greeted by Cap'n Cuttlefish, who recruits them to defeat DJ Octavio and rescue the Great Zapfish along the way. They reappear in the Octo Expansion to help support Cuttlefish but is attacked by the Telephone and briefly hypnotised into battling Agent 8. As of Splatoon 3, they are the captain of the New Squidbeak Splatoon after Cuttlefish's retirement.
Agent 4 - The player character in Splatoon 2 enters Octo Canyon and promptly meets Marie, who gives them a new Hero Suit and entrusts them with finding the missing Great Zapfish and Callie. They eventually found and defeated DJ Octavio, freeing Callie from his mind control and rescuing the Great Zapfish.
These characters have all worked for or with the New Squidbeak Splatoon, but are either not full members, or their full membership status is currently unknown.
Sheldon - As noted by Marie at Cuttlefish Cabin, Sheldon was invited to be part of the New Squidbeak Splatoon in Splatoon 2, but declined, maintaining that the "technology team" must keep distance from the "troops on the front lines". Nevertheless, he still provides assistance, lending Agent 4 several hero weapons and occasionally commenting and giving advice during missions. During the final boss battle, he is seen driving a flying truck with Marie on top, reminiscent of the trucks used during Template:S'Splatfests.
Agent 8 - The first Octoling member of the New Squidbeak Splatoon, they were recruited by Cap'n Cuttlefish when they were knocked into the Deepsea Metro alongside him and Agent 3 by an unknown third party. They escape the depths with the help of Cuttlefish and Off the Hook and later save Inkopolis from being destroyed by Commander Tartar.
Pearl - This Inkling wanted to help out Agent 8 and Cap'n Cuttlefish upon overhearing them in the Deepsea Metro. She did so through giving advice and by cheering, as well as lending Agent 8 some CQ Points when they ran out. She also taught Cap'n Cuttlefish some rapping tips.
Marina - This Octoling also helped Agent 8 and Cap'n Cuttlefish during the Octo Expansion, feeling that she wanted to help her fellow Octoling escape. She did so by giving advice and hacking into the metro's systems when needed.
Trivia
The Squidbeak Splatoon is likely the reason Splatoon is named as such.
'Splatoon' is a portmanteau of 'splat' and 'platoon'.