During Thanos' reign of terror on the universe, Thor travels to Nidavellir with Rocket Racoon and Groot, intending to forge a weapon that can kill Thanos, only to find Eitri the last surviving creature in the area, a giant, metallic ring surrounding a dying star. Eitri accuses Thor and Asgard of not protecting the dwarves during the attack of the Rock Trolls, until Thor reveals that Asgard has been destroyed. Eitri reveals that Thanos forced him to create the Infinity Gauntlet, a device capable of harnessing the powers of all the Infinity Stones, by threatening all his fellow dwarfs. When the gauntlet was completed, Thanos reneged and killed all the dwarfs except Eitri, as well as mutilating his hands in an attempt to prevent him from forging anything else, and absconded with the gauntlet. Thor nonetheless convinces him to build the weapon.
Eitri decides to forge a battle-axe known as Stormbreaker that, as well as having the powers of Mjolnir (except its worthiness enchantment), can also summon the Bifrost. The ring serves as a mechanism that can harness the energy of a dying star to melt a cosmic metal known as Uru, allowing Eitri to make his weapons.
With Thor and Rocket's help, the ring is locked into place to begin harnessing the energy, but the mechanism is crippled, forcing Thor to hold it open and let the energy flow through him, critically injuring himself, in order to allow Eitri to heat the metal. Eitri continues forging the axe, knowing it will save Thor's life, but realizes the handle is missing. Groot uses his tree-extensions as a new handle, thus finishing the axe and allowing Thor to summon it to himself.
Although the axe allows Thor to join his fellow Avengers in Wakanda, the battle, and the entire Infinity War, results in Thanos using the Infinity Stones to disintegrating half of all life in the universe, only for the Hulk to reverse the disintegrations five years later; it is unknown whether Eitri was among the victims.
Powers and Abilities
Dwarf Physiology: As king of Nidavellir, Eitri possesses several superhuman physical attributes common among the dwarves. However, many of these attributes are significantly superior to those possessed by the majority of his race. Like all dwarves, Eitri is much larger than Asgardians and humans respectively.
Superhuman Strength: As a dwarf, Eitri is much stronger than most Asgardians as he was able to send Thor flying with a kick.
Superhuman Longevity: Eitri does not visibly age. He has lived for thousand years, since the days when Odin was once a ruthless war king who conquered the Nine Realms, despite being 5,000 years old, if not older, he still maintains the physical appearance of a man in his prime, thus; Eitri possesses a form of ageless immortality.
Master Engineer: Eitri is a highly skilled blacksmith and forger, as he has forged several weapons and armor for the Asgardians over the years; such as Mjölnir. However, by far his most impressive feat of his blacksmith skills, is that Eitri was able to forge Stormbreaker, an enchanted axe-hammer that exceeds even Mjölnir. According to Eitri, Stormbreaker is the most powerful weapon in the history of Asgard that he has ever created.
In the comics, Eitri is short like the other dwarves, but in the film, he is the size of a giant.