Board Thread:Lore Discussion/@comment-25267426-20150814222841/@comment-9212235-20150815071300

Tiber Septim is not a god, Talos is. There's a difference. Also, he wasn't always a god. Also, no, it's probably not Tiber Septim as he might not have been Dragonborn, until he was. So maybe it was Talos of some variaty. Talos is extremely complicated so I'll stop there.

So who is the doom-driven hero? Auriel? Might make sense. Tsun is shield thane to Shor. Shor son of Shor leaves the possibility of Trinimac, as he is Tsuns mirror. It's also possible it was Reman. That dude got around (wink). The "doom-driven" part always made me think it was a Shezarrine as well as Dragonborn (reference to the Doom Drum). That leaves very few individuals. Pelinal, Reman, Talos, LDB, and any called Ysmir.

Short answer: We don't really know.