The Asgardians are the inhabitants of Asgard. They are a race of extraterrestrial beings similar to the human beings possessing a highly advanced form of technology resembling magic and sorcery, which their entire civilisation is built on.
The Asgardians are a brave and a powerful warrior race whose passion for adventure is their religion, and their reputation as one of the mightiest races in the universe has earned them the respect and fear from other races.
Having interacted with humans in Scandinavia centuries ago, they informed their culture and religion and thus share many characteristics with the ancient Norse. For example, it appears that an Asgardian surname is their father's name and the child's relation, similar to old Norse tradition. For example, Thor, the son of Odin, has the surname Odinson, leading him and other Asgardians to believe this applies to humans as well, exemplified when they refer to Phil Coulson as "Son of Coul".
War against the Dark Elves
Eons ago, Bor, one of the first Kings of Asgard, led his armies in battle against the Dark Elves. Under the rule of Malekith, the Dark Elves set about to destroy the Nine Realms at the time of the Convergence, using an Infinity Stone called the Aether.
Conquering the Nine Realms
Odin led Asgard into a violent conquest of other worldy planets, alongside his daughter, Hela. Together, they ambitiously conquered the Nine Realms. Unsatiated by just the eight planets, Hela wanted more conquest and more power, and so, realising how powerful Hela really was, Odin swiftly banished her from Asgard before she could harm anyone.
To ensure Hela would not return, Odin sent his Valkyries to Hel in order to kill her. However, Hela overpowered the warriors, killing everyone with the exception of Valkyrie.
War against Jotunheim
In 965 AD, the Frost Giants of Jotunheim set about to conquer the Nine Realms, starting with Earth. The Asgardians, now under the rule of Bor's son Odin, arrived in humanity's defense. The Asgardians eventually drove the Frost Giants back to Jotunheim, where Odin personally defeated the Jotun king, Laufey to the point of surrender. After a truce was made, the Asgardians claimed the Casket of Ancient Winters, Jotunheim's greatest weapon, and took it back to Asgard for safekeeping.
While on Jotunheim, Odin found Laufey's abandoned son and decided to raise him as his own alongside his own son, Thor. Odin named the child Loki and planned to eventually use him to unite the two kingdoms and bring about a permanent peace.