He is the Dragon who blood bonded with the crusader Sety during the Miracle of Darna, bestowing upon him the self-named Forseti (tome). As a result of this blood bond, Forseti was thus remembered as the Wind God of Silesse.
Forseti later resurrects Sety's descendent Lewyn after the latter is killed by Manfroy in the aftermath of the horrific Battle of Belhalla. Forseti then proceeds to possess Lewyn, erasing some of his memories in the process. Through the guise of Lewyn, he guides Seliph through his arduous journey to regain peace upon the continent, only revealing the truth of his identity at the end of the events of Fire Emblem: Genealogy of the Holy War.
“I understand now... All my life, I've heard tales of how the dragonkin feared becoming entangled in the sorry affairs of mankind. But you were different... You guided us where your kin never would. So long as our world lives on, humanity will never forget your kindness... Lewyn... No... A hero of a distant land... Forseti of the Wind...” —Seliph, in the Ending of Genealogy of the Holy War