The most explosive and hotly debated event among fans recently in Marvel's Earth-616 mainstream continuity is the revelation that the true identity of the new "Female Thor," who inherited Thor's mantle since the series began last October, is none other than Jane Foster!
Why did this happen? Here, we must first mention last year's major event, "Original Sin." In the story of Original Sin, Uatu the Watcher, who recorded all events in the universe, was murdered, and his eyes were gouged out, revealing the secret pasts of various Marvel characters that they never told anyone, or even didn't know themselves.
▼ Uatu's death, with his eyes gouged out, was quite horrifying... In addition, the killer also stole many powerful artifacts collected by Uatu and confidential data from the MARVEL universe. The Avengers rushed to Uatu's base on the moon to investigate, hoping to find the killer's true identity. 
S.H.I.E.L.D. leader Nick Fury held one of Uatu's eyeballs, because he was the one who killed Uatu. He tricked various heroes into coming to him, and subsequently a great battle ensued. Because Nick possessed the eyeball, he knew all the heroes' secrets. He spoke Tony's password to forcibly deactivate his armor, and when fighting Thor, he rewrote Odin's enchantment, causing Thor to lose his worthiness to wield the hammer. 
After the event, all the Norse gods came to the moon, wanting to understand what had happened to the hammer. Even Thor's father, Odin, couldn't lift the hammer. After the Norse gods dispersed, a mysterious hand touched the hammer and it reacted. It was then revealed that Nick had rewritten the enchantment, making it so only a worthy female could wield it, which, of course, turned out to be Jane Foster, as we now know.
Note: Because recent comics only revealed that Nick rewrote the enchantment so Thor and Odin couldn't lift Mjolnir, but anyone else who is worthy still can, not limited to just females.
Here, we will first introduce the mainstream continuity version of Jane Foster. When Thor was cast down to Earth by Odin to learn humility, he used the identity of a limping doctor named "Donald Blake." Jane was Dr. Donald Blake's hired nurse. Later, the two developed a romantic relationship, but she also fell in love with Thor, who often saved her life. Unaware that the two men she loved were one and the same, she was tormented by a love triangle. Thor later revealed the truth, and as compensation and reward, took her to Asgard, a realm forbidden to mortals.
▼ The film version of Jane Foster was adapted as a scientist, portrayed by Natalie Portman. 
▼ In the original comics, Dr. Donald Blake could transform into Thor by striking his wooden cane on the ground. 
▼ A small Easter egg from the movie "Thor." When Thor infiltrated the temporary S.H.I.E.L.D. base and was arrested, Dr. Erik Selvig prepared a fake ID for Dr. Donald Blake to rescue him. 
Although Odin knew this woman was key to changing his son's arrogant attitude, he still firmly opposed their relationship, primarily because one was a god and the other a mortal. However, Odin eventually softened, deciding to allow Jane to become a goddess, and thus required her to undergo a trial.
But Jane failed. In an unavoidable situation, Odin had no choice but to erase Jane's memories of their shared experiences. As compensation, he arranged for Jane to work under Dr. Keith, Donald's rival, and made them fall in love (this man was good, having once helped Captain America resolve the side effects of the Super-Soldier Serum, and had liked Jane for a long time. Essentially, one cannot become a god without passing the trial, which is why Odin painfully separated his son from her), while Thor reunited with his old love, Sif. 
Jane later faced a near-fatal danger after being possessed by a supernatural entity. Thor was greatly worried and saddened upon learning this, and Sif also realized that Thor still deeply loved Jane. Thus, Sif ultimately decided to merge with Jane to save her life, and Jane also remembered everything about Thor. Afterward, the two separated into distinct individuals again, and Jane subsequently married Keith. From then on, Jane only occasionally appeared when the Avengers needed help.
Finally, Jane became a doctor and helped heal the wounded on Captain America's side during the Civil War event. Even when Spider-Man, who had left Iron Man's faction, was severely injured during a pursuit and eventually brought to Captain America's stronghold by the Punisher, Jane assisted with the surgery. 
Upon Thor's return after the major event "Ragnarok," he learned that Jane had divorced and even lost custody of her child. Although Thor had revived and reawakened many Asgardians, he couldn't find his wife Sif's soul, so he sought out Jane, as the two had once merged. Jane later discovered Sif's soul within an elderly person who was dying of cancer. Thor quickly awakened (resurrected) Sif, and the elderly person passed away as if relieved. Jane's feelings, however, were quite complex.
During the Marvel NOW! era in the mainstream continuity, Thor visited Jane and learned that she had cancer, and her hair had fallen out due to chemotherapy. However, she had a new boyfriend accompanying her, which greatly relieved Thor. Thor then offered to help with treatment using Norse or even Greek divine methods, but Jane refused, stating she wanted to fight cancer as an ordinary human. 
Jane then sought to inherit Thor's spirit, lifting the hammer to become the new Thor, fighting Frost Giants and Dark Elves. Eventually, she reverted from her transformation, returning to a sickly state, and Thor sent her for care. 
However, the major event Secret Wars occurred in 2015, destroying all universes and merging them into a single planet called Battleworld. The Female Thor, transformed from Jane, would fight alongside Thors from different worlds, different times, and different universes. 
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