As the all-seeing Asgarde responsible for guarding the Rainbow Bridge known as Bifrost, Heimdall's perceptive skills serve as his first line of defense.
Guardian and Gatekeeper
Heimdall is an Asgardian warrior who protects Asgard and its denizens by guarding the borders of the realm from his observatory on the Bifrost Bridge. Armed with his incredible broadsword and the ability to see anywhere in the universe at any time, Heimdall ensures that no one who would threaten the kingdom enters it.
When Hela, Odin's firstborn, returns and invades Asgard, Heimdall abandons his gatekeeper post and becomes a heroic force for the kingdom bereft of Odin, Thor and the Warrior Three. He helps Asgardians out of the city and into a fortress built by the elder Asgardians.
Heimdall sees and hears everything thanks to his psychic abilities. His vision can span all of the Nine Realms and from Bifrost Observatory he can see 10 trillion souls. He can hear Asgardians calling to him from other worlds such as Earth, Jotunheim, and Sakaar.
As an Asgarde, he has superhuman strength, speed, durability, and longevity. A master fighter and swordsman - wielding knives and his broadsword Hofund - Heimdall is capable of taking down numerous threats on foot or in the air. He wears incredibly gilded armor and a horned helmet.
He oversees the comings and goings of Asgard via the Bifrost Observatory, which is connected to a rainbow bridge. The Bifrost is an interdimensional gateway to all other realms. Using his sword, Heimdall can direct the Bifrost energy to a desired location, usually one of the other nine realms, including Earth. The energy is drawn from the center of Asgard to the Observatory, where it is directed toward a target and acts as a precise means of transport. Like a tractor beam, its light pulls people and objects back to the observatory. However, this beam of energy that the Bifrost projects project can destroy an empire or planet if allowed to remain open. The bridge can only be activated from the Hofund.
Threats to Asgard
All enemies of Asgard are enemies of Heimdall.
Odin's adopted son and the god of mischief, Loki controls Heimdall and access to the Bifrost when he temporarily becomes ruler of Asgard while his father is in Odin's sleep. He later accuses Heimdall of treason for letting the jotun into Asgard via secret routes, and strips him of his Asgardian citizenship.
Hela, the goddess of death, threatens all of Asgard with her implacable rule. Heimdall defies her and protects escaped Asgardians, leading them to a secret cave under a mountain and protecting them as long as they can all hold out. He later fights her directly to protect her.
Possessing incredible strength and ferocity, the Mad Titan Thanos will stop at nothing to possess all six Infinity Stones. In his quest, Thanos and his followers Ebony Maw, Corvus Glaive, Proxima Midnight, and Cull Obsidian board the Asgardian refugee ship in search of the Space Stone housed in the Tesseract, which was last housed in Odin's Vault. Heimdall tries to help his people face Thanos.
Others who wreak havoc in the Asgardian realm and solidify themselves as Heimdall's enemy include the Frost Giants, the Dark Elves, Marauders, Helas D-Guards, and Surtur.
Thor Odinson, Sif and The Warriors Three come and go from the Bifrost with Heimdall's permission. When away from Asgard, they can call on him to open the bridge. Heimdall only does so if her return does not threaten the eternal kingdom. He has a particularly good relationship with Thor, whom he values not only as heir to the throne of Asgard, but also as a good man.
Heimdall swore an oath to King Odin Borson as guardian of the Bifrost to protect their realm from outside threats. If Odin is temporarily out of service or missing, Heimdall is sworn to the throne of Asgard and whoever sits upon it.
In a battle against Hela and her army, Heimdall allies with Thor and the Revengers - Loki, Valkyrie and Hulk - to ensure the survival and safe escape of the remaining Asgardians from the compromised realm.
Despite his phenomenal ability to see everything, Heimdall failed to see the Frost Giants break into Odin's vault to steal their coffin of old winters. An enraged Thor wanted to face the jotun - an act Odin forbade. Thor, Loki, Sif, and the Warriors Three approached Heimdall to gain access to Jotunheim, which Heimdall allowed out of curiosity. Despite his acceptance and desire to learn how the Jotun had gotten past him, his loyalty to Odin was stronger; he told his king of their departure.
After Odin banished Thor to Earth for his insolence, he fell into Odin's sleep, resulting in Loki's temporary rule over Asgard. During this time, he ordered Heimdall to restrict passage, particularly for those wishing to retrieve Thor, as doing so would violate Odin's final edict. Heimdall reluctantly pledged loyalty to the new king, reminding Sif and the Warriors Three of his loyalty to the throne and that he could not open the bridge; However, he turned his back on them and granted them access to Earth to retrieve Thor. Heimdall learned that there are secret paths that even he is blind to, and it was Loki who allowed the Frost Giants to enter Asgard. Accused of treason, Loki relieved Heimdall of his duties as gatekeeper and stripped him of his Asgardian citizenship.
Thor's battle with the Frost Giants resulted in the destruction of the Bifrost Bridge and Asgard's isolation from the other Nine Realms. However, the Tesseract Cube housing the Space Stone harnessed enough energy to rebuild the Bifrost Bridge and restore contact with the other realms, returning Heimdall to his Gatekeeper post.
When Thor asked Heimdall about Jane Foster's well-being, the all-seeing warrior was unable to find her, prompting Thor to leave Asgard in search of her. After discovering Foster's infection with the Aether, which had the power to rip apart the fabric of reality, Odin restricted access to the Bifrost Bridge.
Foster's presence with the Aether drew Malekith and the Dark Elves to Asgard. Heimdall saw their arrival from Bifrost Observatory, jumped onto their plane and destroyed it with his knives. However, it wasn't enough to stop the approaching horde directly behind. To protect the kingdom, Heimdall incorporated the Hofund into the Bifrost and established a protective shield around Asgard. However, a Dark Elf inside shattered the shield, leaving the palace wide open to attack, resulting in the assassination of Queen Frigga.
Heimdall aided Thor in his secret mission to trick Malekith and rescue Jane Foster, confessing his treachery to Odin and offering his hofund, who looked at him in disappointment, before ordering the einherjar to take Heimdall into custody. During this plan, Loki seemingly perished, but later returned to Asgard and usurped Odin's throne, posing as his father the king.
While Loki ruled Asgard as a false king, Heimdall was banished from Asgard. Skurge was assigned as the Guardian of the Bifrost. With the death of Odin, his firstborn, Hela, the goddess of death, was released from her captivity and went after her two brothers, Thor and Loki. Loki witnessed Hela's desecration of Mjolnir and prompted Skurge to open the Bifrost. Hela followed them back to Asgard but drove them off the bridge.
Upon arriving in Asgard, Hela slew Volstagg and Fandral, who were guarding Bifrost Observatory along with Skurge, to whom she offered the role of her executioner. With Skurge by her side, Hela determined that she was the rightful heir and ruler, and anyone who opposed her was killed. On her way through Asgard's palace, Heimdall infiltrated the observatory and stole Hofund to prevent Hela from influencing the other nine realms. While Hela was distracted, he evacuated the remaining Aesir to a secret underground fortress to protect them from her.
Trapped on Sakaar as a champion contender for the Grandmaster's Gladiator Games, Thor sought Heimdall's help by calling his name. Heimdall allowed Thor to see Asgard through his eyes while they discussed the threat of Hela. With limited time and resources to protect Asgard from Hela and her army, Heimdall told Thor how to escape from Sakaar and find his way home to Asgard.
As Hela and Skurge approached Heimdall's hideout, Thor's arrival served as a diversion for Heimdall to help her people escape Asgard. With the observatory blocked by Fenris and Hela's D-Guards, the Revengers attacked. This allowed Heimdall to help get everyone on Loki and the escaped Sakaar gladiator ship, the Statesman, to safety. After Asgard and the Bifrost Bridge were destroyed by Hela and the resurrected fire demon Surtur, the remaining Asgardians, Heimdall, Thor, Hulk, Valkyrie, Loki, and Sakaar gladiators left their shattered kingdom in search of a new home, only to be lost by one being stopped by an unknown spaceship.
The starship was that of Thanos and his followers Ebony Maw, Cull Obsidian, Proxima Midnight and Corvus Glaive who instantly killed everyone on the Asgardian refugee ship except those who were spared and allowed to escape from the Mad Titan along with Thor, Loki, Hulk and Heimdal. When they all seemed defeated, a wounded Heimdall gathered his remaining dark energy bestowed by Odin to send Hulk back to Earth to warn them of Thanos' quest for the Infinity Stones and impending arrival. For his act of bravery and defiance, Thanos stabbed Heimdall through the chest as the Asgardian warrior gave his king one last look.