Fafnir was once the King of Nastrond, an extradimensional realm on the continent of Asgard. As Fafnir and his people were thoroughly evil, the ruler of Asgard, Odin, destroyed the kingdom and all of Fafnir's subjects. Fafnir himself was left to die in the ruined wasteland that was his former kingdom. However, he found a pool with magical properties, and while drinking from the pool, it transformed him into a massive dragon. Fafnir now possessed strength on par with the Thunder God Thor; a devastating flame breath; the ability to cast illusions and control weak-minded individuals. Fafnir was now almost invulnerable, as his dragon hide was so dense that he barely felt blows from Thor's hammer Mjolnir. It was said that the pool had been formed from the blood of Fafnir Hriedmarson, a Vanir turned into a dragon due to a gold-curse.
Despite these tremendous abilities, Fafnir was never able to defeat Thor. On the first occasion that Fafnir battled Thor, he was sent hurtling into a deep chasm created by a blow from the Thunder God. Before his next encounter with Thor he faced Warriors Three who he seemingly defeated until the Young Gods showed up and rescued them 
On the second occasion he fought Thor, Loki freed and assisted Fafnir against Thor but both were held at bay by the combined might of Mjolnir and the magical Nornstones until the intervention of Odin. On the next occasion, Fafnir was killed by Thor when he used Mjolnir to drive an enchanted spear into Fafnir's heart.
Many years later after the invasion of Asgard by Norman Osborn. Thor, Captain America (Steve Rogers) and Iron Man (Anthony "Tony" Stark) met Fafnir in the Nine Realms turned in Hel and after attempting to torture Tony in order to hurt Thor, he joined up with them in order to defeat Hela who wielded the Twilight Sword and restore balance to the Nine Realms, and as a result he was returned to Hel.
- Superhuman strength, stamina, and durability
- Fire Breath
- Illusion casting
- Mind Control
- 22 appearance(s) of Fafnir (Nastrond) (Earth-616)
- 3 appearance(s) in handbook(s) of Fafnir (Nastrond) (Earth-616)
- 2 mention(s) of Fafnir (Nastrond) (Earth-616)
- 5 mention(s) in handbook(s) of Fafnir (Nastrond) (Earth-616)
- 1 invocation(s) of Fafnir (Nastrond) (Earth-616)
- 2 image(s) of Fafnir (Nastrond) (Earth-616)
- 2 quotation(s) by or about Fafnir (Nastrond) (Earth-616)