Bucky Barnes is one of the most complex characters in the Marvel Cinematic Universe. We were first introduced to Barnes as Steve Rogers protective best friend in Captain America: The First Avenger. He joined the army and served well alongside Rogers until his presumed death. Later it was revealed that Bucky was actually captured by HYDRA, brainwashed and experimented on. HYDRA turned him into a ruthless superpowered assassin by the name of Winter Soldier. From then on, Bucky AKA the Winter Soldier served Hydra until Captain America: Civil War where he was eventually sent to Wakanda for his brain to be fixed.
During his appearance at MCM London, Sebastian Stan who plays Bucky Barnes/Winter Soldier in the MCU was asked what he would do if he had the opportunity to use the Time Stone — which for those who do not know, is the Infinity Stone that has the ability to manipulate time. Interestingly enough, Stan says that Bucky wouldn’t completely reset or erase his history as the Winter Soldier, but will certainly do something to stop all his past assassinations.
“What would Bucky do if he got the Time Stone? Get the hell out of there! [Laughs.] No, if he got the Time Stone, of course, he would go back to face himself in the ’70s and then it would have to be two Winter Soldiers, one against the other, then he would have to face himself and stop himself from creating about 864 assassinations.”
Stan’s answer is interesting. Had Bucky gone back in time to prevent his capture, we wouldn’t have got the Winter Soldier, who since Captain America: Civil War has saved countless lives. By going back and stopping his past self from assassinating anyone and perhaps even convince himself to be good, Winter Soldier could’ve been the hero the world needed for many, many years, especially the years in which his best friend, Captain America was frozen and asleep.