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This topic is for Discussing Factions of Warframe!
Here are short descriptions of all of them!

TENNO


Descendants of warriors from the bygone Orokin era. Following an unspecified war, the surviving Tenno were cryogenically preserved for centuries before being awakened by The Lotus (voiced by Rebecca Ford, community manager of Digital Extremes), a mysterious (though benevolent) figure who guides them during missions. The Tenno are extensively trained in the use of Warframes, suits that grant them various abilities for combat and support.
Bosses: • Lotus •
Assassins: • You •

GRINEER


Fascistic, militaristic brutes who dominate the solar system. Relying on mass cloning and cybernetic enhancement, they primarily use sheer numbers to overwhelm and overpower their foes, occasionally supporting their troops with specialized or heavily armed Forces.
Bosses: Captain Vor • Councilor Vay Hek • General Sargas Ruk  • Kela De Thaym  • Lieutenant Lech Kril • Sprag • Tyl Regor • Ven'kra Tel •
Assassins: • The Grustrag Three •

CORPUS

A proto-corporation who control the trade routes across the solar system and reverse-engineer their technology from any Orokin artifacts or Warframes they find, viewing said artifacts as a resource exploited at any cost. As a result their soldiers—while frail compared to their Grineer counterparts—are equipped with advanced technology and are assisted by sophisticated mechanical drones.
Bosses: • Alad-V • Jackal • Hyena • Raptor •  
Assassins: • Zanuka Hunter •

INFESTED

Don't really have a trailer for this one, but a fan made a montage
Being victims of the "Technocyte Plague"—largely unfortunate Grineer and Corpus soldiers—they have been warped into monstrous abominations. Much like the Grineer, they rely heavily on sheer numbers to overwhelm their targets but lack any significant ranged abilities. Occasionally scattered in the Infested swarms are Ancients, individuals in much more advanced stages of infection and endowed with unique abilities. They invade other faction's ships, including abandoned Orokin ones.
Bosses: • Phorid, Lephantis •
Assassins: • The Stalker •
(in fact, The Stalker avenges all killed bosses of all factions, but he appears like an infested Tenno more than anything else, although his physical features, origin and motivation are still largely unclear. for more info, go to this topic: [You must be registered and logged in to see this link.] )

CORRUPTED
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The enemy itself is the ship/temple. It corrupts trespassers and forces them to protect it. Raiders and trespassers (composed of units from the previous factions) get brainwashed into protecting the Void Orokin Vaults. The corrupted appear cleaner and stronger than their original forms, and are aided by the ships weapons as well, turrets, laser traps and other devices triggered by pressure pads and motion sensors.
Bosses: • Corrupted Captain Vor •
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Let's start the conversation! What would you add to these descriptions? What's your most hated faction enemy? What's your strategy for them? What new faction would you imagine they could add? Bring it!

I would like that the DEvs make more references to Dark Sector. I think you should add the "Sentients" template.