This was an idea I had this morning; the Tenno are not the first.
The Tenno are the second generation of the Void. My idea was that the Tenno get several messages from the Void, from it comes a whispering voice, saying "You think you're the first? You Tenno think you're special? You are far from this..."
This being reveals that his body has long since been dead, now one with the Void, he is a horned creature of glowing smoke, looking like some kind of horrific Void creature that's left it's shell. The creature explains that since the Void is eternal, he is so as well.
Another idea was that the light/dark choices we get from War Within plays some part in this (an idea spawned from TheDsIEGE). My thought was that our choices either lead to something akin to the creature, or something else. And as a side note; we'd get a chance to be one of these Void creatures when fighting him in a boss battle, probably even customize our own in the end. I hope DE takes note of this and uses it as a content concept

Dude do some research on the Void from World of Warcraft.

That's related to the Void in its purest form other than that. That is a good Idea dude.

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Old topic, but I like the concept. Unfortunately, it sounds a little too close to The Man in the Wall, so I don't see DE using it in the same vein as what you're suggesting. But, I like transforming the idea into Void Entities that TMitW could potentially send after you.