Heimdall is a fictional character in the Marvel Comics universe, based loosely on the god Heimdall of Norse myth. He first appeared in a comic in Journey Into Mystery vol. 1 #85.

Heimdall is the brother of the warrior Sif. He is the all-seeing and all-hearing guardian of Asgard, he stands on the rainbow bridge, Bifrost and stands watch for any attacks to Asgard. For ages, he stood as the guardian of Asgard, defending the city's gates from any intruders, and was one of the most trusted servants of Odin. When Asgard was invaded by the fire demon Surtur, Heimdall attempted to defend the gates, but was overcome, and the rainbow bridge was destroyed. No longer needing to be stationary, Heimdall spent more time in Asgard, and became close to Amora the Enchantress, who was soon infatuated with him. When Odin returned to Asgard after Surtur's defeat, he gave a portion of his power to Heimdall to rebuild the rainbow bridge, and Heimdall resumed his duties. Heimdall was gravely injured during the war with Seth, the Egyptian god of death, but he was healed by Odin.

Shortly afterwards, when Odin was about to enter his Odinsleep, he passed the Odinpower on to Heimdall to rule Asgard until he awoke. Heimdall had to deal with a major crisis in the life of Thor, as Thor had been banished into the subconsciousness of the mortal Eric Masterson, who had assumed Thor's responsibilities. Sif was determined to find the real Thor, and her determination drove a wedge between her and Heimdall. When Karnilla conspired with Loki to rule Asgard by having Odin awaken with Loki's soul possessing him, Heimdall was branded a traitor and banished to the Dream Dimension, ruled by the demon Nightmare. During this incident, his mind had been altered, leaving him little more then being able to follow directions. The Enchantress battles Nightmare in order to save him, ultimately rescuing them both. Eric Masterson helped restore Odin and later Thor as well.

Heimdall and Amora drifted apart when Amora realized that his duty to Asgard was greater than his love for her. When Odin cast the Asgardians into the guises of mortals to protect them from a false Ragnarok, Heimdall became Donald Velez, and joined the other "Lost Gods" in attempting to rediscover who they were and battling the Egyptian death-god Seth. Heimdall and the others regained their true forms and defeated Seth just as Asgard was attacked by the Dark Gods, and they were all taken prisoner. They were finally rescued by Thor.

Around this time, Jason, a powerful member of the earth-based team the Pantheon, claims to have eluded Heimdall's senses during a trip through Asgard and over the Rainbow Bridge. Not many people trust Jason.

An alternate reality version of Asgard featured the realm itself floating over the East Coast of America. This raises worship of Thor, who was the ruler and he utililizes Heimdall's senses to hear the prayers directed to him.

Recently, Asgard was struck by another Ragnarok, one from which there was no seeming reversal. Heimdall perishes in battle defending his people.

It has been revealed that Thor has broken the cycle of Ragnarok, the end of all things that has seemingly come to Asgard many times. Heimdall, along with the others of Asgard, have been reborn on Earth yet again. A new version of the city has been established in Nebraska.

Heimdall has the typical powers of an Asgardian god, including superhuman strength, stamina, and durability. He also possesses superhuman senses, most notably his vision and hearing. His senses are said to be so acute that he could hear sap running through trees and see events occurring miles away. Heimdall also briefly possesses the Odinpower, which granted him the power to channel cosmic energies.

Heimdall is an experienced warrior, and a fierce hand-to-hand combatant. Heimdall wields a variety of swords, shields, and spears, and wore a suit of armor. Heimdall bore the Gjallerhorn, which he would sound to alert all of Asgard to dangers threatening the city's gates. While in the mortal form of Donald Velez, he wore enchanted glasses which granted him superhuman vision.

Heimdall appears in the video game Marvel: Ultimate Alliance. He is seen defeated and being guarded by Rhino and Shocker.