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

"The Sentients had won. They had turned our weapons, our technology, against us. The more advanced we became, the greater our losses.  The war was over unless we found a new way.  In our desperation we turned to the Void.  The blinding night, the hellspace where our science and reason failed.

We took the twisted few that had returned from that place. We built a frame around them, a conduit of their affliction. Gave them the weapons of the old ways. Gun and blade. A new warrior, a new code was born. These rejects, these Tenno, became our saviors. Warrior-Gods cast in steel and fury striking our enemies in a way they could never comprehend.

Excalibur was the first."

- Orokin 'Warframe' Archives (Excalibur Codex Entry)

Additional Information
The Tenno are the faction controlled by the players. Each player is a Tenno with a suit of armor called a Warframe. The combat abilities provided by Warframes 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 their mysterious nature, and the ancient Warframe technology that they wear, creates the possibility that they are something more alien.

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

Lotus

 * Main article: Lotus

Upon revival from cryostasis, the Tenno are guided by a figure known as the Lotus. Asserting preservation of her people by any means necessary, the Lotus dispatches and guides Tenno through missions of espionage, sabotage, defense, extermination, and rescue. On these missions, the Lotus guides Tenno using audio commands transmitted from an unknown location. Like the rest of Tenno culture, she remains shrouded in mystery.

Some weapons bear the Lotus emblem to distinguish them as being unique or Tenno-altered, while other weapons bear the symbol simply as a trademark of Tenno construction.

Hostages liberated during Rescue missions appear to be human, and wear jumpsuits that bear the Lotus emblem. It is suspected that these hostages are human, or are unarmored Tenno.

Speculation
The Tenno are mysterious in the extreme, with most details about their lives, origins, and motives unknown. Given this mystery, there is much speculation surrounding many aspects of the Tenno.

The Tenno share the last name with Hayden Tenno, the protagonist of Sector Dark Sector. This was confirmed in Livestream 10: that Hayden is indeed the "first Tenno". His connection to the Tenno in the current time period of Warframe is unknown, but if the confirmation of Hayden being the first Tenno is correct, this implies that a form of the Technocyte virus exists in the Void, where the Pre-Tenno were mutated and corrupted. The two games' settings are different, however, as Hayden is not Infected from the void in Dark Sector.

Considering that the Tenno can be kept in biostasis, require life support, can bleed, breathe, die, and that various NPCs, such as General Sargas Ruk and Lech Kril, refer to Warframes as suits, it is well established that Warframes are suits of armor, and that they contain a living, organic Tenno. (Lech Krill states that there is flesh beneath a Warframe) 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, further solidifies this.

The Tenno themselves are obviously humanoid, with distinct male and female genders, but whether they are actual humans or perhaps even an offshoot is uncertain. The Warframe Cryopods in defense missions contain what appears to be a human-like male, which could possibly be a frameless Tenno frozen in stasis. The Tenno may in fact be Orokin beings, considering that in the lore the orokin personally sent them into the void, and it would be odd if they chose to send another species.

Another lore accurate theory, due to the previous lore obtained from Dark Sector, is that 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 abilities similar to the other.

Trivia

 * Each Tenno behind the Warframes have official concepts and ideas 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. This, along with any other statements the grineer stated in English were later removed when the grineer gained their own language.
 * 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."
 * The moniker "Betrayers" seems to be partially explained by the Stalker's Codex entry, in which he claims that the Tenno slaughtered their masters at the Mercury Terminus in the aftermath of the Great War.
 * Possible note of worth, the Stalker refers to himself, and the others gathered around him as 'lesser guardians' the Orokin still are far more advanced then even the tenno themselves, and infact served them according to that small bit of lore. It's possible to believe that the Tenno were acting under orders to kill the weaker 'models' so to speak of themselves, to clear the way for the Tenno.
 * Tenno (天皇) means in Japanese "Divine Emperor".
 * In the Profit trailer, Alad V insulted the Tenno as "mute peasants" for humor. Although, this is historically true. Ninjitsu was originally practiced by Japanese peasants in order to defend themselves against corrupt landlords who would take their farmlands by brute force. By concealing weapons as farming tools and the familiarization with the sleight of hand, these allowed the peasants to fend off even the strongest of warriors.