The most elite death squad. More kills than anyone in HYDRA history. And that was before the serum.
~ Barnes about the Winter Soldiers.
The Winter Soldiers are supporting antagonists of the 2016 Marvel film Captain America: Civil War.
They were HYDRA's elite group of assassins that were enhanced by a Super Soldier Serum similar to the one that created Captain America and the original Winter Soldier Bucky Barnes.
According to Barnes, the Winter Soldiers were a group of a five assassins (four male and one female) handpicked by Soviet colonel Vasily Karpov to do HYDRA's dirty work around the world. They happen to be capable of detection and have the highest kill count of all HYDRA history, even before they were injected with the Super Soldier Serum. Barnes also stated that are able to take down a country overnight given by their enhanced abilities.
Barnes also confessed that he was tasked by Karpov to train in combat to provide better strength and insight for them. However, as the training exercises were done, Karpov and Barnes were horrified to learn that the Winter Soldiers lost control and initiated a riot against the other HYDRA soldiers, beating them down to their deaths. As such, Karpov is forced to detain the Winter Soldiers in cryogenic chambers to cool their minds down until further orders.
25 years later following the dismantling of HYDRA, Karpov was killed by Helmut Zemo, who steals Karpov's book containing the trigger words to activate the Winter Soldiers. Upon hearing of Zemo's crimes following the Vienna bombings, Barnes (along with Captain America and Iron Man) deduce that Zemo is heading to the Soviet facility where the Winter Soldiers are located, believing that he might unleash them to the world.
Though the three heroes made to the facility, they are surprised to see that all the Winter Soldiers have been shot to their deaths by Zemo, who reveals that his intentions to release the Winter Soldiers was just a ruse to cover his true plan of tearing apart the Avengers to avenge his family (who died at the Avengers' battle against Ultron at Sokovia).
Zemo then revealed exclusive footage of Barnes murdering Howard and Maria Stark after being brainwashed by Karpov, which resulted a fight between a vengeful Iron Man (who wanted to kill Barnes for this) and Captain America (who attempted to defend Barnes). This resulted a stalemate and the Avengers to be officially disbanded, though Zemo ends up being arrested and taken into custody for his crimes despite his success.
The Winter Soldiers about to receive their combat training.
The Winter Soldiers losing control by beating up soldiers to their deaths.
One of the male Winter Soldiers shot to death by Zemo.
Another male Winter Soldier shot to death by Zemo.
The sole female Winter Soldier shot to death by Zemo.