In Norse mythology, Asgard was the home of the Aesir, a branch of Norse gods counterbalanced by the Vanir, who were seen as nature gods. It was connected to Midgard, the earth, by a rainbow bridge called the Bifrost. Asgard was ruled by Odin, the chief of the Norse pantheon as a god of knowledge, lore, and magic. Asgard is said to be destroyed when Ragnarok, the Norse apocalypse, which translates to Doom of the Gods, comes. Loki, an adopted frost giant brother of Odin and a trickster god turned evil, will raise an army of the unworthy dead, along with his three monstrous children: Hel, who rules the unworthy dead, Fenrir, a giant wolf chained in Asgard, and Jormungand, a sea serpent that encircles the earth. Many of the chief gods of Norse mythology, including Loki, Odin, Thor, the god of thunder, Tyr, the god of war, and Heimdall, the ever-watching guard of the Bifrost, will die, and Thor's children will take refuge in the branches of Yggdrasill and come down when the fighting is over to repopulate the earth.