Major Avengers: Endgame spoilers ahead. Avengers: Endgame features countless references to story elements from Marvel Cinematic Universe movies past, paying-off throwaway lines and mysterious moments from the franchise's 22-film history. One callback, however, stands out above all others when it comes to spectacle and sheer power, and that's the moments when Captain America wields Mjolnir, Thor's Hammer in the final fight against Thanos.
Thor's hammer Mjolnir was destroyed by his evil sister Hela in Thor: Ragnarok, but thanks to some manipulation of the Quantum Realm, Thor is able to go back in time, specifically to the events of Thor: The Dark World, and borrow it from that point in history. During the final battle against Thanos's forces he's seen dual-wielding Stormbreaker and Mjolnir, but at some point Thor loses his grip on his trusty hammer. Then, just as it appears that Thanos is going to plunge Stormbreaker into the King of Asgard, Mjolnir flies at Thanos only to return to the hand of one Steve Rogers.
The rules of Mjolnir is that the hammer can only be wielded by those who are deemed worthy of wielding it by the hammer itself. A party game during Avengers: Age of Ultron showed that none of the other Avengers are capable of lifting the hammer as easily as Thor — but Steve Rogers comes close. It only took 11 more films to get there, but Avengers: Endgame shows that there's only one human capable of wielding Mjolnir, and it is Captain America.
Fan reaction to the moment has been mixed so far, with some people saying that the moment was one of the biggest highlights of the entire film (which is no small achievement for a three-hour movie chock-full of memorable moments), while others expressed confusion or disappointment that the franchise didn't seem to follow its own internal logic. While Captain America's ability to not just wield Mjolnir but start throwing lightning around like he'd been doing it his whole life likely startled some viewers, the moment probably wasn't much of a surprise to anyone familiar with Steve Rogers' history in the comics. Rogers has wielded Mjolnir multiple times in the comics. In fact, the Endgame scene where he yells, "Avengers Assemble!" seems to be pulled from a page in Marvel's 2011 Fear Itself event in which Rogers fights with the mighty hammer.
While the shield-and-hammer combination that Captain America wielded during the fight with Thanos is particularly impressive, the end of Endgame makes it clear that the collaboration was a one-time deal. The final moments of Endgame show Captain America going back in time to put the Infinity Stones and Mjolnir back in their rightful place — and he returns a much different man than he left. He doesn't return via time travel, but instead goes back in time to grow old with Peggy Carter. It may not be a godly hammer, but it seems that Steve Rogers would've given up all the weapons and power in the world to have that dance with Peggy he promised so long ago.