Commander Tartar

The Telephone, also known as Commander Tartar during the final boss fight, is the main antagonist in Splatoon 2's Octo Expansion.

Appearance and traits
In its telephone form, it appears as an old-timey telephone box. It frequently uses slang, but also has error messages inside brackets appear in its speech, possibly because it cannot find the correct slang, given that one of the error messages it prints reads [SLANG_NOT_FOUND]. Once Agent 8 has collected all 4 of the thangs, it connects its telephone body to the thangs, transforming itself into a blender. During the final boss battle, it appears as the telephone box with turquoise ooze seeping out, as well as an Octarian tentacle poking out and no longer speaks in slang or error messages. Being an AI, Tartar does not have any major personality traits, though appears to have a hate for what he would deem the less important things in life, such as fashion, sports, etc., and lets Agent 8 know as much before the final boss fight, saying it was "disgusted" by Inkling (and Octoling) culture.

Octo Expansion
The Telephone initially appears as an ancient-looking public telephone in the Deepsea Metro. It provides Agent 8 with two items:
 * 1) The CQ-80, a device through which they control which Deepsea Metro to go to next.
 * 2) The CQ Card, which holds the CQ Points used to enter missions and revive if failing.

The Telephone then tells Agent 8 about the promised land that awaits them outside of the Deepsea Metro, and informs them that they must collect 4 thangs in order to return. Upon gathering all 4 thangs, however, they actually form a massive blender. The Telephone then tries to grind up Agent 8 and Cap'n Cuttlefish into raw materials, only to be stopped by Agent 3, with the Telephone seemingly broken.

During a lengthy escape, the Telephone attacks Cap'n and Agent 3, eventually hijacking the latter's mind into tying up Cap'n and attacking Agent 8. Their hijacked mind is broken when Agent 3 is defeated by Agent 8.

Following the defeat and Agent 8's escape above the surface, a gigantic stone statue emerges. In the hollowed out eye of the statue, the telephone appears and introduces itself as Commander Tartar and declares its intent to eradicate and recreate all life on Earth. The Commander activates a weapon from the statue's mouth; a massive cannon that threatens to destroy the entire world if fully charged.

Agent 8 manages to put a stop to it by inking the entire surface (with the assistance of Marina's Hyperbombs), blocking off the statue's source of power: sunlight. Despite this, the cannon is still able to fire, but is stopped by Pearl's voice-enhanced Killer Wail, with Tartar destroyed along with the statue.

Backstory
Commander Tartar is an AI created by a human scientist referred to only as "the professor" 12,000 years before the events of Splatoon 2. Its purpose was to pass down all of humanity's knowledge to the next capable species. The professor's intention to do so was to prevent the next intelligent species from repeating the same mistakes that lead humanity to extinction. But due to spending all those years isolated and alone, the AI's thought process ended up going in a different direction.

Commander Tartar initially saw hope in the Inklings and Octarians, but eventually became repulsed by their evolution, needless wars, and fashion obsession, ultimately concluding that they were unfit for its knowledge and reprogramming itself to create a new form of life that would be worthy of its patronage, while annihilating the existing lifeforms on Earth. The Sanitized Octarians are its creations, spawned from the biomass it has collected from the remains of its previous test subjects and refined into "the perfect life".

Quotes
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English
When talking to the Telephone after collecting all the thangs and choosing to enter the promised land: }}
 * "Are you ready to visit the Orange S2?"
 * "This is it. Are you [ERROR] ready to ascrend to the higher plane?"
 * "The Orange S2 awaits. Are you ready to join something bigger than yourself?"
 * "Congratulations, number 10,008! The door to the Orange S2 will now open!"
 * "Please, step right inside! Here we go! Do not be shy!"

Trivia

 * Commander Tartar's name is a reference to tartar sauce, a sauce made using mainly mayonnaise, which may again reference the ooze seeping out of it. Tartar sauce is primarily used for seafood, referencing its displeasure for the evolved sea creatures and desire to annihilate them.
 * Tartar's name could also be a reference to Tartarus, a deep abyss far in the underworld in Greek mythology. It would reference how the facility is deep underwater. This may also tie into the possibility that the NILS Statue is meant to resemble the Greek god Hermes.
 * There is a similar looking telephone in Octo Canyon hanging to the side of the cabin in Tentakeel Outpost, showing signs of having rust being in a turquoise color.
 * It was confirmed in the Splatoon 2 Anniversary Famitsu interview that the "professor" Tartar was created by was also Judd's owner. This is referenced in Matchmaker Station, where the crates’ formation and patterns are based off of Judd himself.
 * Commander Tartar's "contemporary speech" mode is only present in the English and Latin American Spanish localizations of Octo Expansion. In other localizations, it wonders if Agent 8 has ever heard of the promised land out loud before explaining what it is.
 * In the NOA Spanish localization, Tartar's "juvenile jargon" mode is demonstrated with an exaggerated use of Mexican slang. The mode is already deactivated by the time Tartar reveals the NILS Statue.
 * Tartar actually hints that it is going to blend up Agent 8 in most of his dialogue.
 * The term it uses for Inkopolis, "promised land", may be actually be a reference to heaven or afterlife. It also calls the promised land a "utopia of light beyond your wildest dreams", supporting this theory.
 * When it first turns on its slang mode, it refers to the player as "home skillet". A skillet is a frying pan, a hint that Tartar is essentially going to "fry up" Agent 8.
 * It says the opportunity to pass tests to eventually get to the promised land is "one in a lifetime".
 * When Agent 8 has collected all the thangs, it asks if they are ready to "ascend to a higher plane" and "join something bigger than yourself".
 * The triumphant music that blares out from the Telephone when it assembles the thangs is in a major key, but just as the player and Cap'n Cuttlefish start to enter, it takes a eerily minor key.
 * When Agent 3's mind is hijacked by the Telephone, they have a transluscent turquoise goo protruding from the side of their head. This goo may be the same substance that sanitized the Octarians seen in the Octo Expansion.
 * It may also be a form assumed by Tartar, which is somewhat consistent with his appearance during the final boss, where goo is seeping out from Tartar's telephone form.
 * The Telephone's quote "Are you ready to join something bigger than yourself?" is similar to the quote spoken by Mr. Grizz "You ready to be part of somethin' bigger than yourself?", which appears when the player visits Grizzco for the first time.
 * This could be theorised as Mr. Grizz being Telephone all along, although after Telephone is defeated, Mr. Grizz does not change, though this could be because Mr. Grizz or the Telephone in this case is using an automatic speech program, which was suggested by the developers in an interview.
 * The developers reveal that Commander Tartar seems to have come to apprecciate Agent 8, finally finding a being it considered excellent, but became angry at Agent 8 when they didn't share its views.
 * This is also hinted in its dialogue where Commander Tartar questions Agent 8's association with the other characters, which implies that Commander Tartar sees Agent 8 differently from the other Inklings and Octolings: "Number 10,008, why are you associating with these superfluous nobodies?"

Names in other languages
Telephone

Tartar