Mjolnir (pronounced myawl-nir) is the enchanted hammer wielded by Thor. It was forged by the dwarf weaponsmiths Brokk and Eitri after a bet with Loki. The name means crusher or grinder.
The Mjolnir weilded by Marvel's Thor was made from the mystical ore Uru. It has a long metal hilt made of Uru and is wrapped in a strip of leather with a thong to secure it around the bearer's hand. Mjolnir means "That Which Smashes". When the dwarves started to build Mjolnir, they used the inner core of a star as a mold and while they were shaping the hammer inside the core, the star went supernova and killed off the dinosaurs. When Mjolnir was finished, Odin first used it to defeat the leader of the Frost Giants, Laufey. Later, Thor received the hammer after proving himself worthy after going through Odin's trials.
"Whosoever holds this hammer, if he be worthy, shall possess the power of THOR"
An old enchantment meaning if Thor was parted for more than 60 seconds he reverted back to Donald Blake causing Mjolnir to be taken away.
During a time when Thor became unworthy and was unable to lift the hammer a new worthy (female) Thor could lift Mjolnir and the inscription changed to: "Whosoever holds this hammer, if she be worthy, shall possess the power of THOR"
In the same way Odinson could lift another hammer from other dimension, which inscription says: "Whosoever holds this hammer, if he be unworthy, shall possess the power of THORR"
As the inscription states, only those deemed worthy by the enchantments of Mjolnir may even lift the hammer. Those who are worthy of wielding Mjolnir gain all of Thor's powers (with the exception of the godblast). Other than Thor, some others who have been able to wield Mjolnir include: Awesome Android, Beta Ray Bill, Captain America, Jane Foster, Red Norvell, Thunderstrike, and Wonder Man. As Thor's ancestry Odin, Bor and Buri can also wield Mjolnir. The cyborg clone of Thor known as Ragnarok was also able to pick up an alternate universe version of Mjolnir when he and the Thunderbolts traveled to another universe.
The ability to wield Mjolnir is not permanent, and may also depend on need. For example, when Thor became Lord of Asgard for a time, he was temporarily unable to pick up Mjolnir for having strayed from his honorable path.
Powers & Abilities
As the inscription states, Mjolnir grants its users "the power of Thor." The most prominent of these powers are flight, shown to reach speeds far in excess of the speed of light, and electrical discharge, often demonstrated by either blasts of lightning or by calling it from the sky. Mjolnir possesses a fraction of the Odin Force, more powerful than the Power Cosmic given to Heralds of Galactus. This weapon has more exotic abilities such as energy absorption and projection, dimensional transportation, the creation of force fields, and the tracking of any being or object to anywhere in time or space. But Thor has rarely called on it to perform in such a fashion. The most powerful attack Mjolnir is capable of channeling is the God-blast (which draws power from Thor's life force, and is an ability inherent only to Thor). This is possible without Mjolnir, but it is less concentrated on a single target. Another powerful attack is the Anti-Force which was said to be able to decimate entire planets in a single blast.
Those who have been deemed worthy to wield Mjolnir in Alternate Realities are:
Adam Warlock, Earth-19141
Alex Power, Earth-5631
Beta Ray Bill, multiple realities
Conan the Barbarian, Earth-83600
Danielle Cage, Earth-807128
Dargo Ktor, Earth-8710
DC's Superman and Wonder Woman have also been portrayed as being able to lift Mjolnir in non-canon inter-company crossovers.
Ultimate Thor's hammer bears little resemblance to its 616 counterpart. The handle of ultimate Mjolnir is longer, and comes to a point at the bottom where there is also a leather thong. Rather than a solid, square block of metal for a hammer, Ultimate Mjolnir's head resembles a hammer on one side, and has an axe blade on the other. Similar to its 616 counterpart, Ultimate Mjolnir's enchantments allow Ultimate Thor to fly, teleport, control and manipulate weather (particularly storms), as well as channel thunder and lightning. Ultimate Thor was revealed to have an arsenal of enchanted weapons, including a hammer that resembles the 616 version of Mjolnir.
Iron Man 2 (2010)
Mjolnir makes an appearance in Iron Man 2. It can be seem at the end of the film after the closing credits, where Agent Coulson is shown reporting its location to Nick Fury.
Mjolnir is featured in the Thor live action movies as Thor's primary weapon. It displayed many attributes common to its comic counterpart such as flight, weather manipulation and electrical discharge. A running gag involves Darcy Lewis mispronouncing Mjolnir's name as "Mew Mew".
The Avengers (2012)
Mjolnir is again featured in The Avengers, where Thor plays a prominent role. It is used effectively against the Hulk and Iron Man but is unable to penetrate Captain America's shield. It demonstrates several abilities, including flight, electrical discharge, weather manipulation, and the ability to return to Thor's hand. Its enchantment also proves strong enough to prevent even the Hulk from lifting it.
Thor: The Dark World (2013)
Mjolnir is once again featured in Thor: The Dark World.
Avengers: Age of Ultron (2015)
Mjolnir returns in Avengers: Age of Ultron. One of the early scenes in the movie features a debate among the Avengers as to whether or not the hammer really is magic. This results in a humorous scene where Captain America, Hawkeye, Iron Man, and War Machine all attempt to lift it. None of them are successful, though Captain America manages to budge it slightly (something which visibly surprises Thor).
Just prior to the final battle, Vision proves himself worthy when he demonstrates the ability to lift the hammer. During a key moment, he lifts it again and uses it to attack Ultron.
Thor: Ragnarok (2017)
Early on in Thor: Ragnarok, the goddess Hela destroys Mjolnir, forcing Thor to rely on other weapons.
Various companies such as Hasbro and efx have produced replicas of the hammer at various price points.