Heim is a character from the background story of Fire Emblem: Genealogy of the Holy War. He is one of the Twelve Crusaders, possessing the title of Saint, and is the original wielder of the Book of Naga. He was known as a "powerful military hero who saved the world".
 Saint Heim is the founder of the country of Grannvale, alongside its capital, Belhalla. While his blood lineage is known as Naga in Genealogy of the Holy War, it is called Heim in Fire Emblem: Thracia 776 instead.
Heim's known blood descendants include Azmur, Kurth, Deirdre, Seliph, Julia, Linoan, and Julius, though Julius did not inherit any Naga holy blood.
The developers notes reveal that Heim became influenced by Naga's will when using the Naga tome, in the same way Lewyn would later do with Forseti.
In Norse mythology, Heimdall was a god who is the guardian of the Bifrost bridge and sees everything in the Nine Realms. He is prophesied to fight Loki during Ragnarok where the two kill each other..
Heim and Naga
from Fire Emblem: Genealogy of the Holy War Sigurd's Tale