Octolings are playable characters in Splatoon 2, alongside the Inklings. Unlike Inklings, which are unlocked from the start, Octolings are only available after beating the Octo Expansion DLC.
Why They Rock
They're very cute.
Just like Inklings, they can swim in ink.
They saved Inkopolis by preventing Commander Tartar's plan to eradicate all Inklings
They spawned funny memes like Oomy and Veemo.
They made friends with Pearl and Marina.
Just like Inklings, they have the ability to shoot their own ink from a variety of different weapons, which makes their games much more creative than the average shooter game.
Also just like Inklings They also have the ability to shapeshift between humanoid and octo form.
They were the main antagonists of the Main Story mode.
They die in water just like Inklings, and like said, in real life, Octopus can swim in water, but Octolings can't.
Agent 8 was first revealed as a character intentionally on March 8, 2018.
They notably look very different from the Octolings seen in the hero modes for Splatoon and Splatoon 2, instead resembling Marina more.
Though Agent 8 exists, there are no Agent 5, 6 or 7, and instead, they're the 10,008th person to try and get to the promised land. 10,008 was to much of a mouthful for Captain Cuttlefish, so he decided to call the octoling Agent 8 as a result.
Apparently, when Agent 8 was in Octarian society, they felt heartbroken at the fact that their superiors were kidnapping the Zapfish and had to refrain from saving them themselves, as shown in the eighth Mem Cake of the Line I series, implying that Agent 8 was possibly more compassionate than other Octolings to start off with.