Tenno

"The Tenno are descendants of an ancient and mystical civilization of lost warriors from the Orokin era on Earth. Preserved in cryopods for centuries, the Tenno now awaken to a new war, fighting and resisting warring factions as the sole bearers of the Orokin-created Warframes.  While the memories of the Tenno have faded over time, their mastery of guns, blades, and Warframe exo-armor has not. Fragments of history suggest that discipline and chivalry are the cornerstone values of the Tenno: is this true today? The Tenno are emerging into a world unfamiliar to them. One sees a noble warrior, building his strength against an oppressive regime. Another sees an opportunistic mercenary, exploiting the Warframe's superiority for wealth. Regardless of their future, the Tenno stand united against a common foe, loyal only to each other."

- Warframe Official Website

Additional Information
The Tenno are the faction controlled by the players. Each player is a Tenno wearing a suit of armor called a Warframe. The Warframes' combat abilities are vastly superior to both the Corpus' high technology and the Grineer's vast numbers; even the most inexperienced Tenno can fight their way through hordes of basic foot soldiers alone, and teams of experienced Tenno can best even the deadliest enemy threats.

Awakening from deep slumber to a hostile world, the Tenno know little of themselves. They appear human, but the mysterious nature of ancient Warframe technology leaves open the possibility that they have undergone extensive genetic or biomechanical enhancements to stay on the edge of progress like the Grineer, or that such modifications may be required to use their Warframes in the first place.

Each Warframe bears one primary weapon, one sidearm, and a melee weapon. Their arsenal includes rifles of various types, shotguns, pistols, swords, and more exotic close range weapons like staves, axes, and power gauntlets. Different classes of Warframes offer their own unique powers, ranging from Volt's burst of superhuman agility to Frost's deadly avalanche, and the armor's modular nature allows for major upgrades and wide customization options. Solitary squads in the field have adapted to wildly different situations using only a moment of downtime between missions.

Lotus
Upon revival from their cryostasis, Tenno take guidance from a figure who simply calls herself Lotus. Asserting preservation of her people by any means necessary, she dispatches and guides Tenno through missions of espionage, sabotage, defense, slaughter, and rescue, but only with audio commands from an unknown location. Like the rest of Tenno culture, she remains shrouded in mystery.

Speculation
The Tenno are mysterious in the extreme, with most of the details about their lives, origins, and motives unknown. Given this uncertainty, speculation surrounds many aspects of the Tenno.

The Tenno share the last name of the protagonist from the first game in the Warframe universe; Hayden Tenno who was confirmed in Livestream 10 that he was indeed, the first Tenno. His connection to the Tenno in the current time period of Warframe is unknown currently. Speculation also exists on the gender, or even the basic humanity of an individual Tenno. In-game text labels the Warframes themselves as having genders. Certain frames have obviously male or female features and are referred to as such in the text, which raises the question of how a Tenno can, for example, change from the bulky, masculine Rhino to the slight, feminine Mag. One hypothesis is that the Tenno are genderless themselves, products of advanced technology and simply appear male or female depending on the armor they wear. It is also possible that Warframes aren't really a suit to be worn, but rather a sort of avatar or artificial proxy body controlled remotely by an operator, and that Tenno are not bound to physical bodies and may freely move their consciousness to whichever Warframe body suits them. Much like the Lotus is a guiding voice to the Tenno, a Tenno might be a compelling force within the minds of blind, deaf, borderline comatose warrior-monks. And most accurate due to the previous lore obtained from the first game, The Tenno are an advanced form of the Technocyte Virus  in which they have developed biological powers through enhancement by the virus such as Hayden's experience and reaction to the Virus causing vast manipulation of his senses and allowing for an extent to strength and abilites similar to the other Tenno.

It is unknown whether or not the hostages rescued in Warframe's Rescue missions are Tenno without warframes on. The hostages appear to be human and wear jumpsuits with helmets. They also carry what appear to be modern-era pistols, but this could be simply an oversight by the developers. Both the male and female rescued hostages bear the sign on the Lotus on their helmet. The only two possibilities are that they are Tenno without warframes on (likely, as Tenno work for the Lotus, and the launchers update notes for when they were added called them Tenno hostages) or that they are Corpus not wearing their traditional armor who have decided to work for the Lotus (unlikely).

Due to Lotus' in-game comment: "Other than you, I can't detect any lifeforms on the ship", which may be heard during extermination missions after all enemies are killed, it can be assumed that some sort of lifeform is inside the warframes. This contradicts with theories of the warframes being avatars controlled remotely (unless of course the warframes are themselves alive, and being controlled by the Tenno).

Trivia

 * Each Tenno behind the Warframes have official concepts and idea's to what they look like as stated by Art Director Mynki in Livestream #4 which may or may not be revealed in the future. These concepts may also be subject to change throughout development.
 * When engaging a Tenno in combat, Female Grineer (Heavy Gunners, Scorpions, and Ballistas) may sometimes say "Tenno are filth!". This appears to be a new addition to Update 9.
 * The Male Grineer sometimes mutter and shout "Tenno scum!" when firing at a Tenno.
 * The Corpus seem to refer to the Tenno as "The Betrayers." At this point in time, it is unknown why.