There is one character in the MCU who without, many events in the Marvel Cinematic Universe would change dramatically. That man is Bucky Barnes. His arc from Captain America: The First Avenger through to Avengers: Infinity War is one of my favourites, as it shows a character who starts being confident, but is knocked back and then works towards finding his place in this new world.
HIS DECISION TO GO BACK TO SLEEP IN WAKANDA SHOWS A MAN STARTING TO OWN HIS PAST, BUT ALSO CONTROL HIS FUTURE.
When we first meet James “Bucky” Barnes, he protects Steve Rogers pre-serum and is also someone that Steve looks up to and wants to emulate. Through the course of the first Captain America film, we see the relationship change as Steve grows into his new powers while Bucky shrinks in the shadow of Steve rather than vice versa. His “death” is also a powerful motivator for Steve to track down the Red Skull to make sure his plan for the Tesseract doesn’t come into play. This works better in the Marvel Cinematic Universe than having Bucky be more faithful to the comics as a Robin-like sidekick.
This change from the source material means that when The Winter Solider is revealed to be Bucky Barnes, it has a lot more emotional impact. He’s someone that Steve has no motivation to fight, or even believed to be alive. There is very little actual development for Bucky in The Winter Solider since he barely has any lines. But there are some outstanding moments to be had with the fight on the Helicarrier, where he starts to realise who Steve is and remember where he came from. The movie ends placing him almost the opposite to Steve, a man out of time who can’t find his way in the world and also doesn’t have the support network of Sam Wilson, Black Widow and the Avengers.
It’s in Civil War that we finally see a progression away from a supporting character to someone who could potentially carry a film (or a shield) in the future. We learn that if Bucky had died on the train journey, Tony might not have been an orphan and therefore, Iron Man might not have ever existed. It is how he deals with the manhunt for him alongside the guilt of his previous actions that carry the emotional weight of the film more than the threat of Zemo. His decision to go back to sleep in Wakanda shows a man starting to own his past, but also control his future.
When next we see Bucky, he is a man at peace with his past and is genuinely happy to see the other Avengers, and especially Steve. It is in this moment that he realises that he is no longer in his shadow but seen as his equal. There have been rumours abound that Sebastian Stan will take up the shield after Chris Evans leaves the MCU, this would be a great move as Bucky could be a different Cap than we have seen before; more ruthless and also not as black and white as Steve can be.