WARNING: Black Panther spoilers follow immediately!
Black Panther has roared into cinemas as part of Marvel's Avengers franchise, and we love that you don't really need to have seen the other Avengers movies to understand everything that happens in this film. Well, almost everything. While there are a handful of characters who showed up in previous Marvel movies, the film's second after-credits scene reunites us with an Avenger antihero we know well: Bucky Barnes, aka the Winter Soldier, aka (now) the "White Wolf" (played by Sebastian Stan).
Of course, before he shows up, Shuri (Letitia Wright) actually references him briefly with a line that may have gone over your head, even if you've seen every Marvel movie. Toward the middle of Black Panther, Everett Ross (Martin Freeman) takes a bullet for Nakia (Lupita Nyong'o), who insists they do everything to save him. She and T'Challa deliver him to tech genius Shuri to repair him — and her reaction is funny and telling. "Another broken white boy to fix," she remarks, looking at his injured body.
So who was the first "broken white boy" Shuri has to fix? Yep: the brainwashed Bucky Barnes. Bucky had last been seen in Captain America: Civil War, first on the run because he's a war criminal, then on the run again because he's framed for King T'Chaka's murder. Even though his name gets cleared for the crime, Bucky still can't trust himself, and in an end credits scene, he goes to Wakanda and returns to the cryogenic sleep that's kept him young until his brainwashing can be cured.
Now we know that it's Shuri who has been working on this cure, and from what we've seen, she's been successful — if he's awake, anyway, something has to have changed to bring him out of the cryogenic sleep. (He does at least seem rested and tan.) So Shuri's earlier joke about having another "broken white boy to fix" connects back to that earlier scene and another Avengers movie. Also: you go, Shuri.