Mjølnir

"Whosoever holds this hammer, if he be worthy, shall possess the power of Thor."

- Odin's enchantment

Mjølnir was Thor's powerful Asgardian enchanted war-hammer. The hammer was destroyed by Hela during a confrontation between her, Thor and Loki.

Creation
"It was made from this special metal from the heart of a dying star."

- Thor to Korg

Mjølnir was forged as a weapon made of Uru in Nidavellir per Odin's request, with the Dwarves using the power of their forge in the heart of a dying star to create it.

Conquering the Nine Realms
During Odin's conquests of the Nine Realms, his eldest daughter, Hela, possessed Mjølnir and with it she helped her father in his battles. Only after Odin locked her up in Hel was Mjølnir taken from her.

New Owner
Sometime before his coronation to the king of Asgard, Thor received Mjølnir. He showed off with it in the coronation. However, the ceremony was interrupted by a group of Frost Giants trying to steal the Casket of Ancient Winters from Odin's Vault. Thor wanted to go to Jotunheim and show the Asgardians' strength to ensure the Giants would never trespass in Asgard again. By using the Bifrost Bridge, Thor, Loki, Lady Sif and the Warriors Three arrived to Jotunheim. After King Laufey mocked him, Thor used the full power of Mjølnir to kill as many Giants as he could and even to kill the Jotunheim Beast.

Thor's Banishment
"I now take from you your power! In the name of my father and his father before, I, Odin Allfather, CAST YOU OUT!"

- Odin to Thor

After the battle against the Frost Giants, destroying the fragile truce between them and the Asgardians, Odin punished Thor by stripping him of his godly powers. Odin exiled Thor to Earth as a mortal, accompanied by his hammer Mjølnir, now protected by an enchantment spoken by Odin so that only a worthy person could wield its power. Both were transported to Puente Antiguo, New Mexico.

Landing on Earth
"Sir. We found it."

- Phil Coulson

An "0-8-4" was reported, an object of unknown origin, by S.H.I.E.L.D. which Agent Phil Coulson investigated. When Agent Phil Coulson arrived to New Mexico, he observed a massive crater created by Mjølnir. He then called Nick Fury to inform him that he found it. Elliot Randolph, an expert in Norse Mythology and a professor of the University of Seville, was used as a consultant. When Thor discovered Mjølnir's nearby location, he attempted to retrieve it from the facility that S.H.I.E.L.D. quickly constructed around the hammer, but he found himself unable to lift it, and was captured. With the help of Erik Selvig, he was freed and resigned himself to his exile on Earth.

Later, Loki, invisible to mortals, came to the facility where he attempted to lift the hammer, but he could not. When he seized the throne of Asgard, he sent the Destroyer to Earth to kill Sif, the Warriors Three, and Thor. The Destroyer attacked and defeated the Asgardian warriors, prompting Thor to sacrifice himself instead. Struck by the Destroyer and near death, Thor's sacrifice proved him worthy to wield Mjølnir. The hammer returned to him, restoring his powers and enabling him to defeat the giant automaton.

Thor returned to Asgard where he stopped Loki's plan to destroy Jotunheim. To do that, he had to destroy the Bifrost Bridge with Mjølnir.

Chitauri Invasion
"You want me to put the hammer down?"

- Thor

Some time later, when Loki reappeared on Earth, Thor came to capture him. Loki was captured by Iron Man and Captain America, but they were not willing to hand him over to Thor. Thor fought against them, but even Mjølnir was powerless against Captain America's Shield.

While in battle against the Hulk, Thor used Mjølnir to knock the Green Goliath off his feet. When Thor threw Mjølnir, the Hulk tried to catch it only to be dragged straight down to the ground with him. Even with all his strength, the Hulk was unable to lift Mjølnir, giving Thor an upper hand in the fight.

After joining forces with the Avengers, Thor used Mjølnir to great effect against the Chitauri Army. It was however unable to disarm the Tesseract. On the battlefield, Thor used Mjølnir to throw lightning at the Chitauri portal, bringing down a Leviathan and to simply kill potentially hundreds of Chitauri.

Return of the Dark Elves
Thor also used Mjølnir against the Marauders during the Marauders' War, notably destroying a Kronan with one hit, as well as the Dark Elves when they invaded Asgard. Mjølnir was also used to throw lightning at Malekith, burning the right side of his face. When dealing with the Aether, Mjølnir's lightning managed to shatter it into shards, only for it to reform later. Mjølnir was also no match against the Kursed Algrim who simply deflected it when Thor summoned it to strike him. Mjølnir, however worked greatly against Malekith on Earth, with Thor being able to deflect many of his Aether powers. The constant shifting of the fighting between worlds caused Thor and the hammer to become separated, but at the battle's apex, as Malekith unleashed the Aether to complete his plan, Thor was able to summon Mjølnir back to his hand and use it to bury the last of Erik Selvig's gravitational devices into Malekith's chest, allowing Jane Foster to transport the Dark Elf warlord to his death on Svartalfheim.

Thinking he was talking to his father (though it was Loki in disguise), Thor offered Mjølnir back to "Odin" who refused it.

Return to the Avengers
"You're all not worthy."

- Thor to the other Avengers

Mjølnir was used by Thor in conjunction with Captain America's Shield during their raid on Wolfgang von Strucker's HYDRA base in Sokovia, with Captain America holding the shield up and Thor hitting the shield with the hammer, causing a shockwave that incapacitated their enemies.

Following the battle, the Avengers organized a party at the Avengers Tower to celebrate the recovery of Loki's Scepter and the defeat of Wolfgang von Strucker. Some of the Avengers played a game to see if anyone could lift Mjølnir. Only Steve Rogers managed to move the hammer slightly, which slightly discomforted Thor.

Running at superspeed, Quicksilver saw Mjølnir fly past him as Thor threw it during the Battle at the Salvage Yard. Planning to use it against the Avengers, Quicksilver grabbed the flying hammer; it dragged him across the facility until he released it. Captain America was able to use that opportunity to knock out the dazed and confused opponent. Acting on a vision he had received, Thor used Mjølnir to recharge the Cradle containing Ultron's incomplete biological body, resulting in the birth of the Vision. A few moments later, as the Avengers were debating whether they could trust him, the Vision easily lifted Mjølnir and casually handed it to Thor. Since the hammer had judged him worthy, Thor accepted the android as an ally and, later, advised he be allowed to continue to be entrusted with the Mind Stone.

Mjølnir was once again used in conjunction with Captain America's Shield to create a combination attack that destroyed many Ultron Sentries as the Battle of Sokovia waged. Captain America would throw his shield and allow Thor to hit it with Mjølnir, causing the shield to fly faster as a projectile weapon.

Vision's ability to use the hammer was utilized during the Ultron Offensive, who of course was not expecting anyone besides Thor to use it. Vision commented that Mjølnir was "terribly well-balanced", which Thor said was necessary so that its wielder did not lose momentum on forward swings.

Destruction
Mjølnir was used by Thor when he was imprisoned in Muspelheim. He summoned his hammer to get free of his shackles and then fought Surtur's army of Fire Demons using it. Upon returning to Asgard, after learning from Surtur that Odin was no longer there, Thor used Mjølnir to threaten the "Odin" impostor to reveal himself, and as he suspected he was revealed to be Loki. The two brothers went to Earth to find their father, so in order to hide it from the public, Mjølnir transformed into an umbrella. Thor was aided by Doctor Strange to find Odin. After the latter located him in Norway, Thor summoned Mjølnir to him, breaking many artifacts of the New York Sanctum in the process. In Norway, before his death, Odin revealed to his sons that they had a sister named Hela who would try to rule Asgard by force after his death. When Hela arrived at their location, Thor threw Mjølnir at her, but she managed to block the attack and hold the hammer with her bare hand. Much to Thor's surprise, Hela destroyed Mjølnir without effort.

Capabilities
"Forged in the heart of a dying star, its power has no equal, as a weapon to destroy or as a tool to build. It is a fitting companion for a king."

- Odin

Thor had been entrusted with the mighty hammer Mjølnir, that was forged in the heart of a dying star. Thor's mystical hammer Mjølnir, which resembled a mallet rather than a war hammer, had a number of elemental powers. It has been stated by Odin himself that Mjølnir's power had no equal, though its power has been contested by the strength of vibranium and the power of the Infinity Stones. Mjølnir was extremely durable and, combined with the various enchantments placed upon it by Odin, it was, for all intents and purposes, indestructible. It had deflected three blasts from the Destroyer (which were able to disintegrate its targets and cause explosions) and returned a blast back to it. Thor often used the hammer as a blunt melee weapon, with almost nothing being capable of withstanding a hammer strike or throw (with the exception of Captain America's Shield). Thor used Mjølnir for a variety of short- and long-range attacks, either by direct hits or by throwing it. It returned to Thor whenever he threw it or summoned it, regardless of the impending obstacles and distance; even traveling through realms. Whenever dropped by Thor, it assumed a fixed position from which no one could move it except for a "worthy" individual. Those worthy of wielding Mjølnir would find swinging the hammer nearly effortless, as Vision stated that it was "terribly well-balanced". Thor also used it for directing his summoned elements, such as lightning, wind, rain, and snow. It was later revealed that Thor's lightning abilities never originated from Mjølnir, but rather it was a tool to help him focus and hone his powers until he was able to master his power and freely wield it. "Every time I threw it, it would always come back to me." "Sounds like you had a pretty special intimate relationship with this hammer."

- Thor and Korg

"When I spun it really fast it gave me the ability to fly." "You rode a hammer?" "No, I didn't ride the hammer." "Hammer ride you on your back?" "No, no I'd spin it fast and it would pull me off -" "Oh my god! The hammer pulled you off?" "The ground! It pulled me off the ground, into the air and I would fly."
 * Weapon Summoning: Mjølnir obeyed Thor's summons as though it were alive. Mjølnir traveled to Thor when it was displaced within a crater from miles away, reaching him in seconds. Mjølnir would return to Thor whenever it was thrown at an opponent. While battling the Hulk in a hanger of the Helicarrier, Thor summoned Mjølnir from another room and it came crashing through the Helicarrier to get to him. After Mjølnir was hurled, Thor was able to change the hammer's direction in flight easily. However, if it is caught by someone worthy and with tremendous strength, Thor would be unable to pull it back to his hand, as evidenced with Hela gripping it preventing Thor from summoning it back.

- Thor and Korg


 * High Speed Flight: Thor was capable of hurling Mjølnir with great force and, by holding onto the leather thong or strap, was capable of flying through the air at tremendous speeds. How fast was not specified, but he was able to remain aloft in the middle of a Class-5 tornado, and traverse the distance from his father's chambers to Heimdall's Observatory and back again in seconds. He used Mjølnir to fly into combat against Iron Man in the woods, to fly to the top of a skyscraper and on top of a Chitauri warship. However, due to Mjølnir's ability to stay airborne only when moving continuously, Thor was unable to stay stationary airborne.
 * Density Manipulation: Mjølnir's enchantment allowed its worthy wielders to swing it nearly effortlessly yet, in reality, it was as heavy as a mountain to an average person. Its ability to manipulate its weight allowed Mjølnir to fly at high speeds without slowing down when hurled as well as have it stricken with a massive concussive force equal to at least that of a grenade. In Jotunheim, Thor bashed the Frost Giants around him with his war hammer, then threw Mjølnir, making it strike multiple Frost Giants in its path in moments. Quicksilver and Hulk were pinned down by Mjølnir's immense weight, as was Loki. Mjølnir's momentum could also be manipulated. If held by someone worthy, its momentum would be that of a simple hammer. If caught and held by someone unworthy in mid-air after being thrown by someone worthy, its momentum would be that of a heavily-weighted object with its velocity unchanged. However, an immensely strong entity could catch it easily without being too overwhelmed by the force, as evidenced when Hela proves to be able to effortlessly catch it and firmly grip it, preventing Thor from pulling it back.
 * Clothing Generation: Mjolnir was able to both conjure armor onto its user, sometimes transforming the clothing already worn by the user into combat attire, which Thor notably used to transform his Asgardian garbs into human street clothes. Additionally, the hammer demonstrated being able to transform and disguise itself to an extent, either through enchantments placed upon it or from its own power, which notably allowed it to transform into an umbrella and then back again. Thor removed these disguises using his lightning when facing Hela.
 * Resurrection: Mjølnir could heal and return people from death, as it was capable of reviving Thor after he was killed by the Destroyer.
 * Energy Blast: With Mjølnir, Odin channeled and projected a powerful blast of energy, using it to remove all of Thor's superhuman powers and destroyed what was left of Thor's armor after stripping most of it off of him, throwing him through the Bifrost Bridge to Earth.

Trivia

 * In the comics, the hammer's name translates as "The Crusher" or "The Grinder". However, in, its name translates as "That which smashes".
 * Odin mentioned that the hammer could also be used as a tool to build, yet no such usage of Mjølnir was seen in the MCU. This was presumably only symbolic, as a hammer could be a tool as well as a weapon.
 * The MCU pronunciation for Mjølnir is ME-ol-near.
 * Darcy Lewis has always mispronounced the hammer's name as "Mew-mew" or "Myeu-muh".
 * In Thor: Ragnarok, Thor disguises Mjølnir as an umbrella and taps it on the ground to change into his armor, the same way that Donald Blake disguised Mjølnir and used it as a walking stick in the comics.