Does anybody know of his orgins? I know he's part Dunmer, Altmer, Bosmer and something unknown. And his mother is speculated to be a Bosmer. Does anybody know or have an idea of where he's from or how he was raised?

And yes I'm aware of the irony.

It's possbile his Native province is High Rock, prior to the Simulacrum Jagar Tharn stole texts from the Brotherhood of Seth/Temple of Sethiete in Camlorn (about powerful magic, and info on the Staff of Chaos) after posing as a Mage-Priest there, which I beleive is the earliest account of his whereabouts prior to the Simulacrum (shortly after this he appears as Nightingale and seduces Barenziah to get the Staff of Chaos).

Afaik, there's no lore on his race, merely theories.

the fact that he was a master illusionist means that nobody is sure what he looks like.

Mhm... I have the not very solid theory, that he is associated with Boethia. His manipulation skill is very impressive. I think, if the were'nt stopped by the nameless hero, he would have betrayed even Mehrunes Dagon (after the destruction of the Battlespire).

A very interesting man.

Not Mehrunes Dagon, Nocturnal's the soft touch

And I doubt he was associated with Boethiah. Mephala or Azura seem, by their spheres, more likely. But by their personalities I highly doubt it.