MCU: 10 Marvel Movie Characters Who've Changed The Most

2. Bucky

In Captain America: The First Avenger, Bucky Barnes is a !*$%-sure, charismatic alpha male who Steve Rogers looks up to and who is presented as the ideal of military personnel (not just by the US Army but also by Rogers). He's a normal, athletic guy sent to war who doesn't allow being captured and tortured to deviate his commitment to the cause or The Howling Commandos.

Then he "dies" and is reborn as The Winter Soldier, a relentless Soviet killing machine repurposed by HYDRA, fitted with augmentations and broken psychologically in catastrophic ways. He was a murderer (under someone else's control admittedly) and didn't recognise his best friend, until Steve saw a flash of what he once was and set about freeing him from HYDRA's brain-washing.

Now, he's still not quite Bucky but he's certainly not The Winter Soldier any more.

What Caused The Changes?

First HYDRA's mind-controlling abuses and his redevelopment into The Winter Soldier: he was stripped of charm, personality and memory and was basically unrecognisable as the good-hearted, arrogant kid from Brooklyn.

And then, Steve Rogers' commitment to their friendship and his willingness to give him a shot at redemption turned him back away from the dark side. He's still changing, but he'll get there.