The Drifter is a playable character as a version of the Tenno from an "unrealized possibility", or alternate reality. Though initially introduced during The New War in Update 31.0 (2021-12-15), the Drifter can be encountered as early as The Duviri Paradox.
Lore & History
The Duviri Paradox
Trapped in the Void's Duviri, in an endless loop of failing to escape from the mad ruler Dominus Thrax, the Drifter is one day mysteriously stabbed before their execution, followed by a strange hand falling from the sky and bonding itself to them. The hand grants them powers, and the ability to control Warframes that have arrived from beyond the Void. The Drifter is led by the hand to Teshin, who offers his 
Sun & Moon and teaches them the ways of the Warframe, explaining the origins of the Tenno and the Zariman Ten Zero ship in Duviri's background. They recover a dismantled toy figure, which Teshin believes will help them escape Duviri. The Drifter sets out to recover the toy's pieces, while peering into Dominus Thrax's emotional states that occurred on the Zariman, supposing him to be one of the ship's children.
Meanwhile, Thrax grows increasingly frustrated by the Drifter's rebellion, and eventually has Teshin captured and killed, dying before the Drifter. Enraged -and thus regaining the emotions they had lost due to the mental strain of their repeated deaths- the Drifter takes control of an Orowyrm and raids Thrax's throne, completing the figurine. Recovering the final memory, they discover that Duviri -and Thrax himself- was inadvertently brought to life from the Tales of Duviri storybook through Conceptual Embodiment by the Drifter themselves, as a result of their emotional anxieties aboard the Zariman. They seize the throne and use its time-rewinding powers to resurrect Teshin, but allow Thrax to keep his power over Duviri, which the Drifter deems to be a fair trade.
No longer shackled by Duviri, the Drifter is now able to leave for the Origin System to repay the aid from beyond the Void's walls. Teshin warns that once they cross over they will not be as who they are now, but as they were then.
The New War
The Drifter eventually makes their way into the Origin System during The New War, which has now been thrown into disarray following Ballas and Narmer's takeover. During the process, the Drifter subsequently lost access the strange hand bonded to them, removing their borrowed capability to Transference like in Duviri. They work together with Ordis to revive the Lotus, and form an unlikely alliance with Hunhow to combat the Archons.
While reviving the Lotus, she fails to recognize the Drifter and turns hostile. They flee long enough for Eternalism to catch up, granting the Drifter Void powers while restoring the Operator, prompting the Lotus to leave. The Operator heads to the Zariman Ten Zero and meets with the Drifter, who explains that they are from a timeline where they were not rescued and were not given the powers of Transference and Warframes. However, the paradox only allows either one of them to continue on to end the threat of The New War.
Zariman Tablets
Within one of the scattered Zariman Tablets discovered in Duviri, there exists an entry implying the existence of an instance during Zariman Void Jump, where the player Tenno accepted their doppelgänger's deal to save everyone, but was the only one not rescued in the process. The exact process of the saving of the other children is left unknown, but the child would be left alone in the Zariman ship adrift in the Void, with no Tenno power inherited from the deal. The adrift child in the ship would soon resort to the Tales of Duviri as a coping mechanism, their emotions and memories reacting with the Void, bringing the Kingdom of Duviri to life via Conceptual Embodiment as an archipelago floating close to the Zariman. That version of the child would become the Drifter.
The Lotus Eaters
The Operator and Drifter meet the Lotus in Sanctum Anatomica. She warns them that she is being influenced by The Man in the Wall who is targeting the former, thus she chooses to send the latter to 1999 and urges them to find Albrecht Entrati.
The Hex
Loid successfully places the Drifter in a loop of New Years Eve 1999, 24 hours prior to Höllvania's nuclear reactor exploding, and it is heavily implied they have went through the loop multiple times. The Drifter briefly possesses Arthur's hand to send him a message to meet under Miras Avenue. Arthur takes the bait, but when the Drifter attempts to perform Transference into Arthur, he refuses it and forcibly ejects them from himself, stabs their hand when they attempt to recover, and brings them back to the Höllvania Central Mall for questioning.
The Drifter explains their story to a mostly disbelieving Hex, but Arthur takes a chance and demands they prove it by finding Entrati. However, when the Drifter does so, they only find the Indifference, and are forced to retreat by a Scaldra ambush.
The Drifter continues to assist the Hex in attempting to stop the reactor from going off, until they find Kalymos, who leads them to a backroom within the mall, where they find a recording from Albrecht. As the time loop has been altered, Albrecht and the Drifter are stuck inside, and in order to escape, must use a spark of energy rare in the time period - the nuclear explosion. As such, if they wish to escape, they cannot allow the Hex to stop the detonation.
However, the Hex learn of the Scaldra escorting a VIP and move to intercept, while Rusalka attempts to intervene. Entrati urges the Drifter to kill her to prevent the Indifference from further influencing the time loop, but they refuse. The Indifference assumes their Operator form and whisks the three away to the Zariman Ten Zero, showing the Drifter that the Hex will die.
The Drifter and Albrecht arrive back in the reactor, with most of the Hex either dead or dying, while Albrecht tells the Drifter to leave to Tau with him. However, they insist that they can save them, with Albrecht replying that they cannot do so "unless you know them," and shoots the Drifter with a 
Lex Prime. As they succumb to their bullet wound, they invoke the power of Duviri to begin another loop - this time encompassing the entire year of 1999.
Finale
Forming personal bonds with the Hex, they attempt stop the reactor explosion again and the Drifter intervenes in their fates. They remind Eleanor that she is not alone, allowing her to overcome the Techrot hivemind and preventing her from attacking Leticia. Quincy's scope is guided to the driver of the H-04 Efervon Tank and shoots first. With encouragement from the Drifter, Aoi realises that she could destroy the machinery controlling the rods and manually insert them back into the reactor while Amir regains his composure and remembers his Parazon to complete the hack. Finally, the Drifter uses Transference on Arthur to pilot his body out of the nuclear reactor's radiation poisoning. Entrati monologues that the Hex could only have been saved had the Drifter allowed their heart to grow. The Drifter returns to the Backroom as the Hex celebrate their victory. Before joining them to celebrate, the Drifter approaches the computer, which displays the message "THE SEQUENCE IS COMPLETE" - indicating that Entrati's plan was a success.
Kinemantik Instant Messaging
Multiple conversations within the chatting session with the Hex reveal personal tidbits about the Drifter themselves. It was revealed in a conversation with Arthur that they have a habit of cutting their food into cube-shaped pieces, likely an ingrained habit from their time living in the Zariman Ten Zero ships which serves nutritional cubes as food.[1] The Drifter has an intense dislike of apathy, as it is what caused them to become stuck in Duviri, and encourages the Hex to continue feeling as to prevent themselves from falling into a similar state.
The Drifter also revealed to Arthur the full story of the Kingdom of Duviri: as a child alone on the Zariman, they used Duviri, which became real thanks to Conceptual Embodiment, as a refuge from the Void. However, while the Drifter could outgrow the world, the world itself could not grow as a result of it being based off of the story. As a result, when they attempted to leave, Dominus Thrax, who considered them his "best friend", would execute them in an attempt to make them stay. Repeated attempts to leave were met with repeated executions, until the Drifter was left apathetic to their situation, having forgotten that they had created Duviri in the first place, and was led to believe that it may eventually end if they simply did not care.
The Drifter can also speak to Quincy about Duviri, who advises them to acknowledge the perspectives of the residents of Duviri, especially that of Thrax, who was faced with his "friend" possibly abandoning him.
Notes
- After the The New War quest, the player can be changed to play as either the Operator or the Drifter via a toggle button on the top right corner when accessing the Operator menu. Most of their armor cosmetics are not shared.
- The roll maneuver for the Drifter uses a standard roll instead of sliding like the Operator, which travels slightly further. The distance travelled by rolling 3 times is roughly similar to an Operator sliding 4 times.
- The Drifter is noticeably taller than the Operator, making them a far bigger target.
- The Drifter can carry a different Amp and set of Arcanes to their Operator counterpart, making for a convenient way of quickly switching to an alternate build when necessary (i.e. a specific build for Eidolon hunts for the Drifter, another specific build for Zariman missions for the Operator).
- The toggle button is not available in the Backroom, as only the Drifter is allowed to appear in Höllvania for story reasons.
- The Drifter can use Operator Arcanes that grant enhancements to Drifter survivability.
- All Amps equipped by the Drifter use the
Sirocco model, even if the skin itself is not equipped.
Trivia
- On their reveal in The Duviri Paradox trailer, the Drifter bared a striking resemblance to Hayden Tenno, the protagonist of Digital Extremes' previous successful video game, Dark Sector. However, Devstream 129 claimed this resemblance was coincidental.
- Even though the Drifter did not have the power of Transference during The New War, Ordis still wishes to call them 'Operator' and they are called 'Tenno' by Hunhow, a term that was given to the Zariman survivors by the Orokin after they were rescued.
- It is implied in the Lost Islands of Duviri Fragments that the Drifter is the only survivor of the Zariman Ten Zero's Void jump accident in their timeline.
- The Hex's nickname for the Drifter, Marty McFlea, is a reference to Marty McFly, the main protagonist of the 1985 film Back to the Future.
- During Arthur's "Hostage Facts" KIM conversation, the Drifter can reveal one of the three facts (or chose not to):
- They repeatedly summoned their childhood bedroom in Duviri in an attempt to hide.
- When they were once decapitated by Lodun, their head flew off hard enough to land in a tree.
- Drifter learned how to ride a Kaithe over six-hundred and eighty-seven loops, breaking multiple bones in the process. It is not clarified if loops refers to individual spirals or a full cycle of all spirals.
- ↑ Drifter on Kinemantik Instant Messaging - "Force of habit. That's how the rations were served on the Zariman, the ship that got stuck in the void. ... So. I guess I do it because there's comfort in it."