Chioma Esi, Ishtar scientist.
Her lover, Maya Sundaresh, is generally the most popular candidate but I believe is incorrect. And I’ll explain why. But for those not familiar with the concept of why Maya could be the exo stranger, I’ll show the logic on why both her and Chioma are the likely candidates, then explain why Chioma is the more likely of the two.
“I was not forged in light”. Right from the in game cut scene. The exo stranger is not a guardian, so that eliminates the candidate pool pretty heavily.
We also know that Exos were once humans, and it is reasonable to conclude that female exos were female humans, and male exos were male humans. Cayde was a human male before becoming an exo. So we are looking for human females, which narrows the list further.
Next step, from Rasputin 4. Now I am 100% sure this card is a conversation between our friendly neighborhood warmind, Rasputin, and our topic of discussion, the Exo Stranger. From that card, a few key words:
“…and you’re certainly not MINE, although once you must have been…”
So what Rasputin is saying here, is that he did not play a role in the exo stranger’s creation as a time traveler. But the “once you must have been” statement indicates Rasputin’s role in the creation of the exos. So he is basically saying, I helped create the Exos, but you are something different that I wasn’t a part of. There is something else he means by “not MINE”. Rasputin assumed control of the Exo’s before the collapse, so in order for the Exo stranger to exist as an Exo, but not be Rasputin’s pin points a time frame in the Golden Age in which the exo stranger must have been created not only as an exo, but also have her time traveling abilities. The Exo Stranger existed before the collapse.
So human female from the golden age is where we look.
Maya and Chioma are among the few known characters that meet that requirement (General Chen Lanshu is another, Old Russia 3, but it can’t be her because Rasputin had already taken control of the Exos by that point). Both were heavily involved in the golden age Vex research on alternate timelines/realities, so that uniquely positions them as being intimately familiar with the very thing the Exo Stranger can do: time travel. They were the ones who uploaded 227 copies of themselves into the Vex network (along with two other scientists). And we know from Cayde’s journal, that in his early days as an Exo, he knew Maya, so she was aware of the Exos. Maya was doing research on the Device, which is the one that lets people view other timelines. So female, check. Golden age, check. Familiar with Exos, check. Timeline researcher, check. And at the end of the Vex 5 card, Maya personally enters the Device. She makes a lot of sense. Except she is not the Exo Stranger.
She is not because:
1) She wasn’t an exo when she entered the device.
2) The device doesn’t allow time travel, just allows people to view other timelines.
So why does Chioma make more sense? Read the first few lines of Vex 5, Maya was sending her log notes to Chioma. So reading those notes, Chioma would have known that Maya put herself in the machine and that it probably killed her. And that the reason Maya entered the device was she was looking for one of those 227 copies of Chioma in another timeline out of loneliness, since they had been apart so long.
Also, Chioma is noted as working on another project, somewhere far away, called Hyperion. There is no discussion anywhere in grimoire about what the Hyperion project is. But we know Bungie likes easter eggs, and Hyperion is a popular sci fi novel about….. Time travel. Possibly?
So Chioma, upon finding out that her lover, her wife actually, entered the device looking for her, would be uniquely positioned with the technology (Hyperion if my speculation is correct), the motivation (find her wife), and the equipment (Exo technology) to fix it.
What I think happened is Chioma in finding out Maya was gone, took on an Exo form (recognizing from her previous Vex research and from Maya’s logs, that the human mind was too weak to survive the time travel) and used her Hyperion project to go find Maya in time. I made another post about the Exo Stranger 2 card. One thing that is interesting about that card that I didn’t touch on in that post, is that the tone of all the journal entries isn’t “I’m a badass, veteran, time traveling warrior here to push back the darkness”, which is the way she comes across in the in game cut scenes. The entries are like she is just coming to learn about the darkness, the Hive, the Vex, and how they all inter relate. As if that is not the reason why she was traveling through time, but more like something she started to discover [i] after[/i] she started traveling through time. I think it is because fighting the darkness is not the original purpose of the Exo Stranger.
It was originally because she was looking for Maya. Now for some true speculation on my part. I think as Chioma sought out Maya, she started to experience what the people who entered the device saw: everything ending in darkness. In time, her purpose changed. I think it changed because she encountered someone else who was very interested in the Vex and the darkness, Osiris. I think they allied together and are still working on stopping the darkness.
I do think Chioma found Maya by the way. Maybe one of the 227 Chioma’s had met one of the 227 Mayas, and the Exo Stranger Chioma let them be and answered the higher purpose (fighting the darkness). Or maybe since the darkness always won, Chioma realized she had to stop the darkness to save Maya.
Regardless, this is why I believe Chioma is the exo stranger. She meets the grimoire requirements and has the motivation. And lastly, her personality seems to fit better too. Maya seemed too…timid. But as they say in Vex 4, as the escaped the Vex simulation, Chioma is the leader.
That's a good theory, but it can't be her only goal. Remember on Venus, the Stranger says "Hold position, kill the engines and don't let them find you.", if she was only with Maya, that wouldn't make much sense and she entered the machine alone, not with backup. So who is she talking to?
Unless she's been through many events in order to reach Maya, then that would make sense. I'm thinking she might be related to Praedyth. Since his dead corpse is found in a hidden area near a chest, she could have been in the Vault of Glass and helped Praedyth, which would explain the "Hold position, kill the engines and don't let them find you" quote. Also the fact that VOG lore plays with the past and the Vex populate it. Now, i'm not 100% sure she was related to him, as there are no 'engines' in VOG, unless they she means oracles or Vex plates. However, i think the No Time To Explain might have been his gun. He might have given it to her or the Stranger took it with the remains of his death. Because The Stranger's Rifle is really similar to No Time To Explain. And you can't find it in VOG loots, so it was either taken or given to her. Also the fact that she says "I don't even have time to explain why I don't have time to explain." Clearly exposing No Time To Explain and the fact that she time travels.
Also, not all Exos were once humans. Exos were war machines created back in the day for the wars. Within time, Exos were considered complex enough to hold a human's life, memory, intel, etc. But there are many unknown reasons why some humans were transferred into an exo body. Some were to be saved and forget, some were because they had the possibility such as perhaps Chioma here and Cayde was to pay his debt to Clovis Bray.
Also, Exos get rebooted instantly after the process from human to Exo. The reboots are just so they forget their past and focus on the present and future. Since they're machines after all, too much memory leads to a reboot. The numbers next to an Exo's name are the number of reboots they received. Like Cayde-6, six reboots. Banshee-44, forty four reboots. Reboots occur to all Exo, guardian or not.
Now, since we don't know the Stranger's amounts of reboots, we can be sure she has at least 1 from being turned into an Exo.
So going back to what the Stranger's goals are, can't just be to save Maya. I'd only assume so for the lines she says, like "Too late, returning. How many?" and "I will. I will. I know." Also because we know she could have been a scientist as you say, so wanting to discover about the Guardian, the Light, the enemy races out of curiosity makes sense.
So she must have someone with her also aware that they're in the past. So it could be Maya but most probably be someone else. As the person the Stranger's talking to, knows about the Guardian and his/her's goals.
In conclusion, it's just one big clusterphuck that leads to more possibilities xD