Warning: now you know this post is full of spoilers for Avengers: Endgame. Don't read any further if you don't want to read them!
We first meet Natasha "Nat" Romanoff in 2010's Iron Man 2, the sequel to the film that kicked off the MCU. Of course, back then she was masquerading as Natalie Rushman, Tony Stark's new personal assistant, with a head full of red curls and the ability to flip a man twice her size without breaking a sweat. When Nick Fury arrives to reveal that she's actually a S.H.I.E.L.D agent — which explains why such a badass would want to be Tony Stark's personal assistant in the first place — it sets the tone for the beginning of the MCU and our love for Scarlett Johansson's Russian spy.
Nat is one of the first Avegners introduced in the MCU, and she's also one of the first of them to die in Avengers: Endgame. In the group's effort to reverse Thanos's snap and bring back their friend, they retrace their own steps in previous MCU films to find the Infinity stones before Thanos collects them all in Avengers: Infinity War. The entire group has been attempting to handle their grief in their own ways and Nat's way is to watch over the scattered heroes attempting to keep the universe safe, similar to her former mentor Nick Fury. When the chance to bring back their friends comes via the arrival of Scott Lang, Nat jumps in with both feet, quickly becoming obsessed with the idea of reversing the snap.
Tony figures out how to perfect time travel using the Quantum Realm, and the available Avengers are able to go back to select points in time where they can collect the Infinity Stones before Thanos does. Nat and Clint (aka Hawkeye) are the ones who go after the Soul Stone in Vormir, which they don't know comes with the price of trading a soul for a soul (which we find out in Infinity War when Thanos sacrifices his daughter Gamora).
The two former assassins argue about who's going to go over the cliff, with Nat and Clint both insisting it should be themselves. After struggling, Nat tells Clint that "it's OK" to let her go, and he reluctantly lets go as she plummets to her death. Clint wakes up with the Soul Stone in his hand and his best friend gone. Later, when all the stones have been collected in Tony's custom-made Iron Gauntlet, Hulk snaps to bring all those previously dusted back. Though he succeeds, he later admits to Steve that he tried to will Nat back with everyone else. But, like Gamora, her death occurred before the stones were collected and thus cannot be reversed.
Though Endgame definitively ends Nat's journey (in that timeline anyway), fans may be wondering what this means for the stand-alone Black Widow film currently in the works — never fear, that's definitely still happening!
Since Marvel obviously loves a prequel, the Black Widow movie will actually take place in the early 2000s. We'll meet Natasha before her introduction in Iron Man 2 and see a bit of the superspy's origin story, as well as how she came to work with S.H.I.E.L.D.
Nat's story may have ended in Endgame, but that doesn't mean there isn't more for us to explore. There's no premiere date for the Black Widow movie just yet, but we're definitely looking forward to seeing Nat back on our screens sooner rather than later.