The Aesir is a pantheon of Norse Gods found in God of War. In Norse Mythology, the Aesir are one of two major factions of Gods (alongside the Vanir). They are hated by the Jötnar (Giants) who hid their realm from the Aesir since the King of the Aesir, Odin, coveted the Giants' ability to foresee the future.
The oncoming apocalypse, Ragnarök, is expected to cause an ultimate battle that results in the deaths of many of the Aesir.