Talos is three people. A Breton, Nord and Imperial. The part of him commonly known as Tiber Septim is a Breton.

Is Tiber Septim a Breton?

The Bretons of Alcaire see Tiber Septim as Hjalti Early-Beard, native to the island kingdom of High Rock. They believe Tiber Septim was a Breton. General consensus holds that not only was Tiber Septim not a descendant of Reman (the previous Empire's progenitor), but that he wasn't even of Cyrodiilic stock.

Do Bretons believe in Talos?

The Bretons have a pantheon of 12 (mer and man) but no Talos figure. Breton? Yes, Hjalti was born in Alcaire, but his race never was stated. Also his fullname 'Hjalti Early-Beard' suggest belonging to nordic culture.