The Nine Realms are a group of vastly distant celestial bodies that are interconnected by the cosmic nexus Yggdrasil, and are home to various different races and cultures.
The Nine Realms are nine individual planets that, while located separate parts of the universe, are systematically connected by the branches of Yggdrasil and orbit Midgard. The inhabitants of the realms are mostly associated with each other rather than the other advanced species residing beyond the realms. Earth, where humanity resides, is one of the Nine Realms, but its inhabitants are considered to be too underdeveloped by the other races to associate with.
Asgard was considered to be the head of the Nine Realms, and its inhabitants, the Asgardians, are arguably the most powerful species in the realms. Odin, the former ruler of Asgard, and his troops act as the protectors of the Nine Realms and even other regions of space. They act as a police force that tries to preserve peace. The Asgardians produced a sister race which settled on the planet Vanaheim, and are referred to as the Vanir. Nidavellir, home of the Dwarves, neighbors Asgard, and a strong relationship is present between the two. The world of Alfheim also lies close to Asgard.
Slightly below Asgard is Jotunheim, which is inhabited by the Jotuns, also known as the Frost Giants. The Frost Giants have tried to conquer the other realms a number of times, but were thwarted in each attempt by the Asgardians. Located above Asgard is Muspelheim, a world that is bathed entirely in flames and is home to many beasts that manifest from the fires. Located at the bottom of Yggdrasil are Svartalfheim and Niflheim. The former was once home to the Dark Elves before a cataclysmic battle against the Asgardians ravaged the planet's surface and nearly drove the species extinct. The latter is a world notable for being the location of Hel, a shadowy area that the Asgardians believe holds the souls of those in the Nine Realms who have died.
Every five-thousand years, an event called the Convergence would take place in Yggdrasil where the spatial boundaries between the Nine Realms gradually decrease until becoming almost non-existent. This would result in the formation of portals between the worlds.
Heimdall of Asgard watches over the Nine Realms and other regions of space. He mentions to Thor that from his post at his observatory he can see nine realms and ten trillion souls. This is the approximate number of inhabitants throughout the Nine Realms or in the region of space the Asgardians preside over.
The Asgardians preside and watch over not only the Nine Realms, but other planets too. Therefore, many species of the Nine Realms have had history of contact with species and civilizations from beyond the Nine Realms.
Thousands of years ago Hela, the Goddess of Death and heir to Asgard, was imprisoned in Hel by Odin after she attempted to seize the throne of Asgard when Odin transitioned into a peaceful king after the Subjugation of the Nine Realms. Her prison was tied to life of Odin, as long as he lived she would remain in Hel.
However, Odin would eventually reach the end of his life, and after an emotional farewell with his sons, he passed on. His death brought about the release of Hela, who quickly arrived on Earth. Hela easily defeated her brothers, forcing them to retreat in the Bifrost Bridge.
After Hela followed and knocked them out of the bridge, she then arrived on Asgard and slaughtered the army. Hela revived an undead army of Berserkers to assist her in reconquering the Nine Realms but discovered that Hofund, the sword the controlled the Bifrost, was missing. She punished the people of Asgard until one stepped forward and gave her the location of Hofund. However, Heimdall managed to escape her along with the remaining Asgardian population.
Hela sent her army after them but Thor and Loki returned to foil her conquest. They successfully evacuated the Asgardians onto the Statesman and unleashed Surtur, triggering the end of Asgard. Hela was killed in the destruction and the surviving Asgardians migrated to Earth to build and settle on New Asgard.
- Population: Asgardians
- Description: Asgard was one of the Nine Realms and was the home to the Asgardians, a powerful race recognized by the galaxy as honorable and brave peacekeepers. It was destroyed by Surtur in order to defeat Hela and enact Ragnarök.
- Population: Humans and Inhumans
- Several leaders of different Nations
- Description: Earth is the third planet from the Sun in its solar system. It is home to the Humans, Inhumans, a number of Asgardian immigrants, and is one of the Nine Realms aligned by the cosmic nexus, Yggdrasil. The various races of the Nine Realms refer to Earth as "Midgard," while those living beyond the realms call it "Terra" and the Kree Empire classify it as "Planet C-53." Earth orbits around a single sun and has only one permanent natural satellite, named Luna, though usually simply called the Moon.
- Population: Jotuns
- Laufey †
- Description: Jotunheim is one of the Nine Realms and is home to the Frost Giants. The planet is seen to be deteriorating from the lack of ice magic that comes from the Casket of Ancient Winters.
- Population: Harudheeniksel
- Malekith †
- Description: Svartalfheim is one of the Nine Realms and is home to the Dark Elves. The Asgardians and other inhabitants of the Nine Realms refer to it as the "Dark World," while the Dark Elves themselves call it "Harudheen". Located in a star system that is almost completely corroded with dark matter, both Svartalfheim and the Dark Elves inhabiting it have developed under a more diverse table of elements. The only source of visible light for the world is a black hole.
- Population: Vanir
- Description: Vanaheim is one of the Nine Realms and is home to the Vanir.
- Population: Dwarves
- Description: Nidavellir is one of the Nine Realms and is home to the Dwarves.
- Population: Fire Demons and Fire Dragons.
- Surtur †
- Description: Muspelheim is one of the Nine Realms and is home to the Fire Demons and Fire Dragons.
- Population: Light Elves
- Description: Alfheim is one of the Nine Realms and is home to the Light Elves.