Spoilers ahead. As much as Black Panther is its own movie separate from the Avengers franchise in the Marvel Cinematic Universe, it would be foolish to think that no other Avengers show up at some point in the film. Bucky Barnes, a.k.a. The Winter Soldier, appears in the second post-credits scene of the newest MCU film, but is Bucky good? Black Panther shows him walking around Wakanda, not killing people thanks to Hydra brainwashing, so one assumes that he's on the mend. Still, if there's any character in the MCU that can turn at the drop of a dime, it's Bucky, which leaves his intentions questionable at best.
Fans last saw Bucky Barnes in a post-credits scene for Captain America: Civil War. After being triggered by Zemo causing a violent spree, going up against Iron Man, and learning that he killed Tony Starks parents, Bucky decided it was best for everyone if he was put back in a suspended state, essentially frozen, until he could be cured. T'Challa, having learned that Bucky was not, in fact, responsible for his father's death, decided to take him in, and pledged to Captain America that he would use Wakandan technology to try to help his best friend. And, in Black Panther, it looks like whatever they were doing worked.
Bucky shows no signs of violence in the Black Panther post-credits scene. He's calm, collected, and even integrated into Wakanda — kids even call him "White Wolf." Shuri, T'Challa's sister, has been taking care of him, using her genius intellect to attempt to deprogram him and rehabilitate his mind. Considering the fact that she trusts him enough to let him roam free amongst children, it certainly seems like he's getting better.
Granted, Bucky being free of Hydra mind control doesn't necessarily mean he's good. He could, after all, have some persona demons that turn him into a super villain of some sort, but that's extremely unlikely. For one thing, Bucky is incredibly loyal to Captain America, something he proved in Civil War, and he had the presence of mind to put himself to sleep to avoid hurting anyone else, which implies good intentions. And then there's Avengers: Infinity War. Early trailers for the upcoming Avengers film show Bucky fighting alongside Captain America and Black Panther in Wakanda, confirming what Bucky fans have always known: he's a good man at heart.
Now that we've established Bucky is good, the next logical question is: what does this mean for Bucky's future in the MCU? Well, in the comics Bucky takes over as Captain America after the death of Steve Rogers, something that has been rumored to potentially happen soon in the MCU. Actor Sebastian Stan has spoken about this possibility many times, noting that Bucky would have to prove himself and regain trust if he ever wanted to be considered America's hero. "There's this issue where we've got to get him to be trustworthy enough for them to give him that responsibility," he told fans at Wizard World St. Louis, via ComicBookMovie.com. "So, I think it's possible, I really do, but it just has to make sense and we might need a little more time."
If Bucky does not become the next Captain America, there is another hero he could be in line for: the White Wolf. The name the kids in Wakanda call him in Black Panther is actually the name of a different Marvel character, Hunter, a white man who, in the comics, was adopted by T'Chaka, T'Challa's father. In the comics, he became a mercenary known as the White Wolf who sometimes helped the Black Panther protect Wakanda despite their tense relationship. It's unclear whether Hunter exists in the MCU, but it's possible that if he doesn't, the nickname given to Bucky in Black Panther could mean that he will take up the role of the White Wolf on screen.
Of course, Bucky could simply remain the Winter Soldier for the foreseeable future. As long as he's fighting on the side of good and not Hydra, he can wear any name he wants.