Board Thread:Lore Discussion/@comment-25267426-20150814222841/@comment-1600847-20160721182333

Bethesda themselves like to confuse us about Tiber Septim's race.

In one Imperial Library article written by Bethesda, they say he's a Breton. In another one, they say he's an Atmoran. In a painting of Tiber from TES Redguard, he's shown as a Nibenean Imperial.

Moral of the story: we're not supposed to know Tiber's exact race. He's human, and that's the closest we'll likely get.