The hammer was used extensively by Thor as his primary weapon until it was destroyed by Hela in 2017. The broken pieces were eventually made into a tourist attraction in New Asgard.
In Avengers: Endgame, Thor steals Mjölnir from his past self (since Hela destroyed it in Thor: Ragnarok) and brings it to the present.
Hela Is Simply More Powerful Than Mjolnir
We know Thor wasn't as powerful as the older and more experienced Hela, which is why Mjolnir still felt like it was superior to him. But Hela made the hammer seem inferior, suggesting she might have stopped Mjolnir, held it, and then shattered it with her raw strength.
Thor's love, and the power imbued in his oath, was so strong that Mjolnir could defy its death and repair itself to fulfill a promise and help Jane. Perhaps Mjolnir could've even repaired itself all along, but it didn't because it was waiting specifically for Jane.
Other than Thor and Odin, certain other individuals have proven worthy of lifting Mjolnir in the primary continuity: Roger "Red" Norvell (a deliberate ruse by Odin) Beta Ray Bill. Buri (also known as Tiwaz, Thor's great-grandfather)
This led Jane to New Asgard, where the broken pieces of Mjolnir were held. Up until this point, no one had used Mjolnir — not even Thor, who likely believed that nothing could put the destroyed hammer back together. Jane's arrival in New Asgard woke up Mjolnir, allowing it to reform to transform Jane into Mighty Thor.
Mjolnir is a hammer, and was enchanted by Thor's father, Odin, so that only those the hammer deemed "worthy" are capable of wielding or even lifting it. Stormbreaker is an axe, and although it does not have such a worthiness enchantment, its power is such that a mere mortal attempting to wield it would be driven mad.
Could Hela destroy Stormbreaker like she did Mjolnir? Not likely. Stormbreaker took the brunt of all six Infinity Stones and kept on going. Mjolnir was a conduit for Thor's powers and had even previously been wielded by Hela.
The Asgardian Son of Odin was extremely close to ending Thanos at the end of Avengers: Infinity War. After gaining the powerful weapon Stormbreaker, Thor becomes the wielder of the most powerful weapon in the universe. Stormbreaker is capable of killing Thanos outright, and only Thor is currently worthy of wielding it.
We rated the strength of each Avenger on a scale of 1 to 10, using evidence from the 23 movies. Scarlet Witch was ranked the strongest. Captain Marvel and Thor rounded out the top three.
Stormbreaker is jealous about Mjölnir's return because the ax is basically a moody teenager. In Thor: Love & Thunder, Chris Hemsworth's Thor comes face to face with somebody he once loved.
Mjolnir was forged for Thor Odinson's grandfather by the dwarves, who used the core of a star and Uru metal to form the iconic hammer and imbue it with its immense strength and magic. It is nearly invulnerable and is capable of great destruction.
Stormbreaker can be used by anyone, it isn't bound by Odin's enchantments to only be lifted by the worthy. Mjolnir is, however, still enchanted, meaning that only those that are worthy may wield it.
The movie doesn't explain Thor's motivations for giving up Stormbreaker, but it makes sense that Chris Hemsworth simply wanted Love to have a powerful weapon to aid her in battle. It's unlikely that he could give her Mjolnir, considering that so few people in the MCU have been deemed worthy of its power.
The chemotherapy is attacking the cancerous cells but Mjolnir doesn't identify the cancer as an illness just as another part of her it needs to protect. Plus chemotherapy really does weaken Jane and make her sick so it's easy to see as an illness on it's own.
In a moment of wistful affection for his girlfriend, Thor asked his trusty hammer to always protect Jane, and in doing so unwittingly enchanted Mjolnir to do just that. Just like Thor's father Odin once enchanted the hammer to only be lifted by someone who is worthy, Thor cast a spell that let Jane use its powers.
However, the film also implies that the hammer only sees Jane as worthy because Thor unintentionally revised the rules of Mjölnir, giving it the power to protect her. Captain America didn't need anything special for the hammer to see him as worthy – he's able to wield it without issue in Avengers: Endgame.
Thor's hammer Mjolnir was defined by the fact that only the 'worthy' could lift it – so basically no-one except the god of thunder (and Vision, for some reason). But when it comes to the weapon's replacement, Stormbreaker – which Thor forges in Avengers: Infinity War – Groot is able to lift it too.
Thor Odinson initially suspects Jane might be this new hero. But he eliminates her from his list of suspects because she is going through chemotherapy for breast cancer, which, he reasons, would make her too weak to fight.
During a Vudu Viewing Party for Avengers: Infinity War, co-directors Anthony and Joe Russo revealed a key difference between Thor's hammer Mjolnir and his new ax Stormbreaker: the latter doesn't require worthiness. That's why Groot was able to lift the ax, not because he was worthy but because he didn't need to be.
He also possesses superhuman strength, speed, agility, durability and immunity to most diseases. Thor's greatest weapon, and closest ally, is Mjolnir, an enchanted hammer forged from Uru metal, which has power over storms and can generate energy blasts known as anti-force.
Jarnbjorn. A battle axe favored by the current unworthy Odinson. It may not be Mjölnir but it has more that proven itself over the past few months. No longer the Thunder God or not, this Thor still has the ability to wreck shop with the best of them thanks to this impressive bit of metal.
Determination. Thor is known for having a bad temper, yet his determination is also among his biggest flaws. Thor's perseverance is a weakness since it puts his life in danger because he continues putting himself in dangerous situations.
The hammer Stormbreaker is very similar to Mjolnir, made of mystic Uru metal and is nearly indestructible. Worthiness: Just like the original Mjolnir, no one can lift Stormbreaker who is not worthy.
How did Thanos manage to lift Stormbreaker? Thanos was able to lift Stormbreaker because the axe doesn't have worthiness enchantment as Mjlolnir does. Mjolnir is specific when it comes to the wielder's might since the only prerequisite to wielding is that the wielder is “worthy” of its might.