Asgard first appeared in Journey into Mystery #85 (Oct. 1962).
According to Asgardian legend, in the beginning there was nothing, but in time two worlds came into being on opposite sides of the void. The one to the north was named Niflheim, a world of clouds and shadows in whose center surged the fountain Hvergelmir, from which flowed twelve rivers of ice. The one to the south was named Muspelheim, which teemed with rivers of fire. Eventually the warm air from the south carved out the frost giant Ymir from the ice in the north. Ymir became the father of all the giants, and his cow Auðumbla licked out of the ice the first Asgardian, Buri. Buri had a son named Borr, who married the giantess Bestla. Borr and Bestla had three sons named Odin, Vili, and Ve, who were known as the Æsir. Odin and his brothers grew to hate the giants and slew Ymir, and his blood formed a great sea. Odin and his brothers then raised Ymir's body from the sea and created Midgard between Niflheim and Muspelheim. With Ymir's bones they created mountains, and with his hair they created trees. They then raised Ymir's skull upon four pillars to create the heavens. Within the skull contained sparks from Muspelheim, which became the sun, moon, and stars. When Midgard was complete, Odin and his brothers created a home for themselves above it called Asgard. Between the two worlds they stretched a rainbow bridge and called it Bifröst.
Once a year Odin must undertake the Odinsleep to regain his strength. During this time Asgard is vulnerable to attack from its many enemies, most notably Odin's adopted son, Loki. Loki first takes command of Asgard during the Odinsleep, using his right as the 'son' of Odin before Thor could claim it, but fled when Asgard was invaded by Mangog as he realized that this new foe was too powerful. Loki later usurped the throne of Asgard by taking the Odinring, but fled again when Asgard was invaded by the fire demon, Surtur.
The throne of Asgard later passes to Thor after Odin is killed in battle by Surtur, when the demon invades Earth. It was prophesied that Loki would lead Asgard's enemies in a final conflict known as Ragnarök, which would lead to its destruction. This comes to pass when Loki obtains the forge that created Mjolnir and creates new uru hammers for his army. The entirety of Asgard and its inhabitants are destroyed in the resulting battle.
After Ragnarök, Donald Blake awakens [Thor 3](movie:956858) from the "Void of Non-Existence". Thor returns to Earth and rebuilds Asgard outside of Broxton, Oklahoma, purchasing the land with gold from the treasury. Thor then goes about restoring the Asgardians, who have been reborn in the bodies of mortal men and women.
Asgard's location on Earth makes the city a target during the Secret Invasion by the Skrulls led by a Super-Skrull named Godkiller, whose powers mimic Thundra, Titania, Volcana and Battleaxe. The aliens are repelled with help from Thor's ally, Beta Ray Bill.
When Thor is forced to abdicate the throne and is exiled for killing his grandfather Borr, who was brought from the past and driven mad by Loki, control of Asgard passes to Thor's half-brother, Balder.
Asgard is destroyed yet again after Norman Osborn seizes control of S.H.I.E.L.D. following the Secret Invasion as he seeks to expel Asgard from U.S. soil in an effort to consolidate power. Osborn leads the Dark Avengers in an invasion against Asgard known as the Siege. The invading forces are defeated with help from the reunited Avengers, although Asgard itself is toppled by the Sentry. Immediately following the Siege, Thor reerects Heimdall's observatory atop Stark Tower as sign of solidarity with Midgard and appreciation for the Avengers' aid.
Thor restores Odin to the throne when the nine realms are invaded by "the World Eaters". However after Thor and Odin's long-forgotten brother, Cul, kill each other in battle during the Fear Itself event, Odin passes control of Asgard to the Vanir, headed by the "All-Mother", a triumvirate of female deities consisting of Freyja, Gaea and Idunn. Tony Stark's company, Stark Resilient then rebuilds Asgard over Broxton, Oklahoma, where it is rechristened as "Asgardia".
The Asgardian Realm is part of The Nine Worlds. The Nine Worlds are connected by the branches of Yggsdrasil, the Tree of Life.
1. Alfheim: Home of the Light Elves (Ljósálfar). Alfheim is a distinct region on the Asgard planetoid.
2. Asgard: Home of the Asgardians. Asgard is the name of the planetoid, a distinct region on the planetoid and its capital city.
3. Hel: Realm of the dead who are neither honored nor dishonored. Ruled by Hela.
4. Jotunheim: Home of the Giants (Jotunn).
5. Midgard: Midgard is the Earthly plane of existence. Although technically not a part of the Asgardian dimension, it is considered one of the Nine Worlds by the Asgardians because of its significant connections to Asgard.
6. Muspelheim: Home of the Demons. Ruled by Surtur.
7. Nidavellir: Home of the Dwarves. Nidavellir is a distinct region on the Asgard planetoid.
8. Svartalfheim: Home of the Dark Elves (Svartálfar).
9. Vanaheim: Home of the Vanir who are the sister race of the Asgardians. Vanaheim is a distinct region on the Asgard planetoid.
Other realms include:
1. Niffleheim: Realm of the dishonored dead which is distinct but closely connected to Hel.
2. Valhalla: Realm of the honored dead and is a distinct region on the Asgard planetoid.