Octarian

The Octarians are a race of octopus creatures and the main antagonistic species of the story mode in Splatoon. They reside in Octo Valley, and are responsible for stealing Zapfish from Inkopolis. Their main ink color is purple/magenta. At one point the Octarians were a neutral species coexisting with Inklings, but this ended as result of conflicting interests of territory that lead to the beginning of the Great Turf War (in which the Octarians lost).

Unlike Inklings, the species includes a great amount of sub-species that act differently from each other. Like Inklings, certain Octarians can switch between mollusk form and humanoid form at will.

DJ Octavio

 * DJ Octavio (Leader)

Bosses of Hero Mode (Splatoon 2)

 * Octo Oven
 * Octo Samurai
 * Octo Shower
 * Neo Octostomp

Others

 * Marina (Octoling, member of Off the Hook, and Show Host)
 * Agent 8 (Octoling)
 * The bass of Chirpy Chips

Types of Octarians

 * Octotrooper
 * Shielded Octotrooper
 * Octodiver
 * Twintacle Octotrooper
 * Deluxe Twintacle Octotrooper
 * Octocopter
 * Deluxe Octocopter
 * Octoball
 * Octosniper
 * Octobomber
 * Deluxe Octobomber
 * Octostamp
 * Octostriker
 * Octohurler
 * Octoseeker
 * Octozeppelin
 * Octoling
 * Tentakook
 * Octocommander
 * Octobowler

Machines

 * Squee-G
 * Flooder
 * Octopod
 * Giant Squee-G
 * Octostamp DX

Great Octoweapons

 * The Octostomp
 * The Octonozzle
 * The Octowhirl
 * The Octomaw
 * The Octobot King

In the manga series
In the end of the fan-made issue of Splatoon, a then unnamed Glasses-Kun flies over a bunch of Octotroopers and Octoballs. It's most likely that they would not appear in the manga again, but might possibly do so due to the Inkopolis Tower not having the Great Zapfish on it in the manga.