Mjölnir (commonly written without diacritics as Mjolnir) and Stormbreaker, in the Marvel Cinematic Universe (MCU), are sentient enchanted weapons of choice used by Thor.

Both are melee weapons and were created out of Uru metal forged with the heat of a dying star in the Dwarven kingdom of Nidavellir, with the assistance of the dwarf king and master weapon-maker Eitri.

Mjolnir debuted in print in the Marvel Comics title Journey into Mystery #83 (Aug. 1962), being the means by which physician Donald Blake transformed into thunder god Thor Odinson (by striking it on the ground).

[1] In a 2002 documentary with Kevin Smith, Lee says his brother and co-creator Larry Lieber originally referred to Mjolnir as the "Uru Hammer".

[4] In a 2018 interview with Jimmy Kimmel, Thor actor Chris Hemsworth revealed that he has kept a number of the prop hammers created for the film.

[6] Meinerding intentionally made Stormbreaker comparatively oversized and overpowered, to convey that the wielder of the weapon must also be someone incredibly powerful.

[7] Both weapons also appear to have a degree of sentience, with Stormbreaker apparently being envious of Thor's affection for Mjolnir,[8] a characteristic director Taika Waititi attributed to the handle being made from the arm of the adolescent Groot, and carrying over some of that character's moodiness at that age.

Over one thousand years later, Mjolnir is seen in Odin's vault alongside other artifacts, and it is wielded by Thor against Frost Giants on Jotunheim.

Thor re-ignites a war between the Frost Giants and Asgard, and Odin banishes him to Earth, stripped of superhuman abilities.

Upon the death of Odin, Hela escapes from her prison, and thwarts Thor's attempt to use Mjolnir against her by destroying it with her bare hand.

In 2018, Thor travels to Nidavellir with Guardians of the Galaxy members Rocket and Groot to request dwarf king Eitri forge a replacement for Mjolnir.

Eitri reveals a plan to create Stormbreaker, an axe with powers similar to Mjolnir and the ability to summon the Bifröst.

Thor joins the Avengers in the Time Heist into the Quantum Realm traveling to an alternate 2013 Asgard to retrieve the Reality Stone.

[13] In the film, a flashback reveals that years earlier, Thor unknowingly enchanted Mjolnir to protect Foster.

She travels to New Asgard in search of the remnants of Mjolnir, which reassembles itself in Jane's presence and proclaims her worthy, surprising Thor when he meets her again as the new wielder of the hammer.

Thor, Foster, and Valkyrie pursue Gorr to the Shadow Realm, where Foster sees ancient drawings that depict Thor's battle-axe Stormbreaker as a way to summon the Bifrost to enter the realm of a godlike celestial called Eternity, who can grant Gorr's wish to destroy all gods.

For unexplained reasons, Thor remains the only one able to lift the hammer in this universe despite Odin never being shown enchanting it with the "worthy" spell.

[19] When Thor's mother, Frigga, arrives to check on him, and he pretends to have been studying Earth culture the entire time, his ruse is revealed when he summons Mjolnir, which is covered with paint, party beads, and a pair of underwear.

In the second episode of the second season of What If…?, Thor is fighting with Mjolnir alongside a team formed by Howard Stark and Peggy Carter in 1988 against Peter Quill and his father, Ego.

In the ninth episode, it is revealed that Strange Supreme has been collecting heroes and villains from various universes to feed to a magical forge, including multiple of versions of Thor.