The last time fans saw Bucky Barnes, AKA Winter Soldier, was during the end credit scene in Captain America: Civil War, where he's shown in a frozen state under the care of Wakanda.
Because of that, fans assumed he'd be up and running in Black Panther—especially since we've seen him ready to kick ass in the Avengers: Infinity War trailer. However (spoiler alert for the three people who haven't seen the film yet), Bucky isn't seen at all throughout Black Panther. That is, until the final end credit scene, where he emerges to meet a bunch of children (who call him White Wolf), along with Shuri, who tells him that he has a lot to learn. Before that, the only reference to Bucky came when FBI agent Everett Ross came into Shur's lab and she called him "another broken white boy to fix."
Now, Black Panther director Ryan Coogler is explaining why he decided to keep Bucky out of the narrative.
"Bucky would have horrible PTSD, he would need spiritual guidance. The last thing he would need to do is jump into that civil war, and so that was kind of the thought process there," Coogler told Collider. "And it could be potentially problematic if it’s a bunch of Africans fighting and you bring in a white dude, he comes in shootin’ people [laughs]. We were aware of that. Bucky’s not trained to neutralize people peacefully, he's an assassin. We were like, 'I don’t know if we can do that…'"
Luckily, we now know that Bucky will return in Infinity War, which is set to premiere on May 4.