In a moment of wistful affection for his girlfriend, Thor asked his trusty hammer to always protect Jane, and in doing so unwittingly enchanted
When wielding Mjolnir, Foster gains all the powers of Thor, including the base Asgardian traits of superhuman strength, speed, stamina, and durability, as well as Thor's flight and control over lightning; though only a tiny portion of those powers.
Indeed, the hammer calls to Jane (Natalie Portman), who is undergoing chemotherapy to treat Stage 4 cancer. The hammer, which can be picked up by those it deems “worthy,” helps her transform into Thor and gives her health and strength—at least for a time.
It's her cancer diagnosis and her struggles with chemotherapy that make her worthy to wield Mjolnir in the comics, given that her powers block the treatment, and the cancer progresses every time Jane Foster wields Thor's power – yet she persists to fulfil the role the universe needs her to, and this may unfold ...
Turns out, she was always worthy because, as Thor reflects, it was Jane who reminded him back in the 2011 MCU film what it meant to be a worthy hero.
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.
The whole idea was to give picking up the hammer a new downside. It made for a very poignant story, along with an unworthy Odinson and the War Thor. This was explained way back in Thor #1, or Journey into Mystery #1 or whatever it was. It was set up this way so that Mjolnir would not cure Donald Blake's broken leg.
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.
Originally there was no restriction placed on the hammer for who can use it but after Thor's reckless behavior, Odin Borson placed an enchantment on it. This spell read "Whosoever holds this hammer, if he be worthy, shall possess the power of Thor." Only those deemed worthy to lift Mjolnir can.
In the comics, she is still suffering from cancer, but is chosen by the hammer Mjolnir after Thor loses the ability to wield it in battle.
Thor can wield both Mjolnir and Stormbreaker without dying, or it causes him to strain his health. It is unfortunate, but the fact that being mortal is what kills Jane for being Mighty Thor makes the original Thor Odinson more powerful.
She was a breast cancer victim until she discovered Mjolnir and its transformational qualities. Because she knew there was an end in sight, she was able to push herself even harder. Even in her immortal Thor body, she's aware of her own humanity, and that's what makes her stronger than Odin.
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.
Mysteriously, the broken pieces of Mjolnir, the hammer of the thunder god, transformed her into the Mighty Thor and gifted her the superpowers of Thor, to battle threats internal and external. Wielding Mjolnir herself, she had become a godly protector and a new hero was born!
3 She Controls Electricity On Her Own, No Mjolnir Needed!
However, even when she doesn't have this weapon, she can create and throw lightning bolts. For instance, she's able to conjure lightning from the inside of a frost giant's head in Thor #3 in order to escape the monster.
In Norse mythology, the hammer Mjolnir is simply too heavy for anyone other than Thor to lift, but over the centuries, the story evolved and even super-strong entities couldn't lift the weapon.
Odin seals Mjolnir after failing to control its power. When Odin first tried to wield Mjolnir, he couldn't control it due to the God Tempest still retaining its power. The hammer devastated Asgard as it flew out of control. Out of spite, Odin cast an enchantment on the hammer to prevent anyone else from wielding it.
Odin sent the hammer to Earth with Thor so that by the time Thor was worthy, his hammer would be waiting for him. Odin needed to know that Thor was worthy to have his hammer, and he wanted Thor to get his hammer back eventually so that's why he put an enchantment on the hammer and sent it to Midgard.
But due to Thor's confidence issues after its destruction, there was a brief window where Jane could have inadvertently conjured the lightning into Mjolnir again. In that window where Thor was hammerless, her own will could have pulled the pieces back together and been the reason that she became the new wielder.
That version of Mjolnir was shattered in the final battle, but its fragments reformed into Undrjarn the All-Weapon, a magical vambrace that could shapeshift into any weapon Jane wanted.
Is Thor still worthy in Thor: Love and Thunder? It is pretty clear that Mjolnir chose Jane, not because Thor was unworthy, but because Thor's oath had instructed it do so. Sadly, the hammer cannot cure Jane's cancer, and can only transform and temporarily empower her.
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.
Can anyone lift Stormbreaker? Yes — and the reasons why a crucial point in the comparison between Stormbreaker vs Mjolnir with respect to Thor's character arc in the MCU. The God of Thunder went through a massive transformation in Taika Waititi's Thor: Ragnarok, which continued into Thor: Love and Thunder.
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.
Jane was told by Doctor Strange that if she became Thor one last time, she would die. He and several of her friends convinced Jane to give up being Thor for the sake of her health.