Ymir was formed at the beginning of creation in a place called Niffleheim. He is an ancient being of limited intelligence. The oldest and most powerful of the Frost Giants, he tends to focus all of his energies towards destruction and little else. This may in fact be Ymir’s only weakness, and the reason why Odin and his two brothers, Ville and Ve, were able to first defeat him.
Except for Surtur, Ymir is the oldest known being in the “Nine Worlds” of the Asgardian realm. The Frost Giants origin is lost in antiquity; however, they are known to predate the gods of Asgard themselves. Few in number due to the heavy losses sustained over the millennia in battle with the gods, the Frost Giants dwell in the frozen land of Niffleheim north of the country of Asgard proper. Their huge size, durability, and raw power make them the gods most formidable foes.
Age has not diminished Ymir’s power in the least. Although possessing some intelligence and capable of speech, Ymir is not particularly cunning or subtly motivated. His vast physical power has enabled him to survive and maintain his rule over his kinsmen over the millennia.