Ahem.....Spoliers.
I've completed the campaign, but not everyone has.
[spoiler]I doubt he's an Ahamkara....but I think he's showing that the conflict we're engaged in is much older and much wider than just the races we've been battling for the last 4 years.
I suspect that Riven is some being that is a servant of the Darkness or the Deep that has somehow become trapped in the Ascendant Realm....and was taking advantage of the chaos that Oryx's death has created. to stage his own jailbreak.
Remember one of his lines to Uldren is, [i]"Even Paradise is a prison if you can't leave." [/i][/spoiler]
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