Story and History

Dark Sector Era

On earth during the cold war, the United States invented something called the Technocyte virus. It remained unused and mostly untested for a number of decades until a 'The Agency', essentially the CIA, sends a submarine with infected aboard it to the Russian island of Lasaria. A member of The Agency, Robert Mezner, is believed to be responsible for either Technocyte's creation or most of its evolution as he is a scientist that specializes in 'nanotechnology as it applies to bioenhancement'. Mezner is sent to Lasaria secretly by The Agency to test and propagate the virus among its citizens.

Mezner goes AWOL and The Agency sends in agent Hayden Tenno to kill him. Hayden knew little to nothing about the virus/Mezner and knew only that he was getting booster shots from other Agency agents to supposedly prevent him from getting infected. Of course, Hayden quickly confronts and nearly kills Mezner when he is attacked by Nemesis, essentially a prototype Warframe that looks like a mix between Rhino and Nyx that is 'piloted' by a woman Hayden knew from the past who is working with Mezner. Nemesis infects Hayden with the same strain of the Technocyte virus that has infected Mezner.

At this point, most of the game of Dark Sector plays out. Hayden reacts uniquely to the virus as it only mutates his right arm/shoulder visibly. For other humans, the pain quickly drives them to insanity and they mutate into horrible monsters (much like the Infested) with techno/organic parts. Hayden also has congenital analgesia which makes him not feel pain, something that most likely was one of the reasons the virus didn't drive him mad.

At the end of the story, Hayden acquires a Warframe (that uses the same character model as Excalibur), defeats Nemesis and Mezner and survives the traitorus Agency but the Technocyte virus ends up being released into the world.

The virus wreaked havoc on all fauna on the planet. Hayden Tenno is the only one know to have assimilated with it and use it to his advantage but as the story ends, we can't be sure if others didn't have similar reactions.

Orokin Era

Flash forward potentially a few thousand years. A race called the Orokin exists. They were either robots/AIs created by the remnants of humanity or a totally alien race that showed up in the solar system (still presumably robots/AIs). For a time, the Orokin ruled the solar system and spent a great deal of time experimenting on genetic remnants of creatures found on earth. From these remnants, post-humans were recreated. There were also failed experiments (like the Desert Skates found in the new tileset) but the experiment that was the most important was the creation of the race known as the Tenno. As Hayden Tenno was 'the first Tenno', they were either created from Hayden's adapted strain of the virus or descendents of his that carried the altered virus and similar genes. The Tenno were named for him.

The Tenno were unique among the new races in that they possessed a vastly superior ability to interface with technology due to their possessing the Technocyte virus. The Orokin created Warframes for the Tenno to use, body armor made from Technocyte material. This gave them the ability to don the armored suits and have great power and physical enhancements.

From here, things get a bit less specific. It is most likely the the Tenno are responsible for the fall of the Orokin via the events known as (and referred to as) The Old War which was followed by The Collapse. It is for this reason the Corpus refer to the Tenno as 'the Betrayers', as the Corpus worship the Orokin and the technology they can salvage from them.

After The Collapse, humanity split in four major directions. The Tenno went into cryosleep for unknown reasons. The Technocyte virus was either still present from its ancient days on earth or was re-released when the Orokins were defeated as much of the recreated humanity became the Infested. It is also possible that the Orokin re-released a Technocyte virus similar to the one that originally ravaged earth in an attempt to combat 'The Sentients' during the Old War. Some of the post-humans took to cloning themselves to create armies and due to a flaw in the cloning process, they took on mechanical enhancements and became the Grineer. The Corpus were certainly the most tech-savvy of the post-humans as they became a 'Merchant Cult' that worshiped money and relics from the Old War.

Warframe Era

Flash forward a few hundred years. The Corpus control most of the resources, shipping and such in the solar system via trade routes known as Solar Rails. The Grineer both fight with the Corpus for power and buy technology from them to support their constantly degrading bodies. The infested spread to a number of different locations on many planets. It is now that the game of Warframe takes place. The Tenno are being woken up by an group (and entity) known as The Lotus and subsequently, other Tenno. Presumably as a byproduct of the defrosting/revival process, the Tenno that are waking have little to no memory of the past.

The Lotus is an organization that leads and organizes the revived Tenno, mostly through a female entity known also as The Lotus. It is possible that The Lotus are AI and descendants or related to the Orokin. The Lotus emblem also adorns some warframes (such as on top of Excalibur's helmet) meaning the Lotus had to exist during the Orokin times when the Warframes were created.

Side note: There is additional evidence that the Orokin were/are machines or AIs. They referred to their enemies in the Old War as 'the sentients', a distinction that would only be given by a non-sentient yet somehow intelligent race. Additionally, the Orokin towers we invade in the Void are filled with hapless Infested, Corpus and Grineer that entered the tower and had a computer chip-like device implanted in them which allows an entity known as the Neural Sentry in each tower to control them and use them to defend the tower and its secrets.