"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."
- -Official Description
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 rifle, 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.
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.
One such aspect is the gender, or even the basic humanity of 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.