He is the Dragon who blood bonded with the crusader Ced during the Miracle of Darna, bestowing upon him the self-named tome. As a result of this blood bond, Forseti was thus remembered as the Wind God of Silesse.
Forseti later resurrects Ced's descendant Lewyn after the latter is killed by Manfroy in the aftermath of the horrific Battle of Belhalla. Forseti then proceeds to make a Geas with Lewyn. As a result of the pact, Lewyn is bound to follow Forseti's will and guides Seliph through his arduous journey to regain peace upon the continent, with the truth of his identity being revealed 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