Board Thread:Lore Discussion/@comment-26893431-20160824210343/@comment-1600847-20180129171125

Tiber Septim's race seems to be a running joke between Bethesda and the fans. He's been referred to by Bethesda or shown as an Imperial, a Nord, a Breton, an Atmoran, and the painting you see of him in TES: Redguard, you could even make the argument he's a paler-than-usual Redguard.

The answer to the question "What race was Tiber Septim" depends on who at Bethesda answers, and what mood they're in at that particular time.

He was human, that's likely the closest we'll ever get. Unless Bethesda decides to troll us and make him a shapeshifting Sload or something.