Winter Soldier

The Winter Soldier is a Marvel megavillain and an enemy to Captain America. He was originally known as Bucky who was both a close friend and sidekick to Steve Rogers/Captain America during World War II, but during their last mission together, Bucky was declared dead; he was later revealed to be reprogramed as a Soviet assassin.

As Bucky
As James Buchanan Barnes, aka Bucky, he lost his father during WWII and was adopted by Camp Lehigh. It was there that he learned the identity of Captain America. He was trained by Captain America and was assigned to be Cap's sidekick. There he accompanyed him on many adventures, and the duo usually worked with the original Invaders.

However, on thier final mission together against Baron Zemo, both Bucky and Cap hopped on an experimental drone plane in an attempt to disarm a bomb. When the bomb detonated, It forced Cap to fall in the North Atlantic, where he would later be found frozen in time and thawed out by the Avengers. The American forces never did find Bucky's body, and he was presumed dead. Not knowing that Bucky was both found and revived by Russian General; Vasily Karpov.

As Winter Soldier
When Bucky awoke, he had no memory of his real identity, which gave Karpov an opportunity to reprogram Bucky as a Soviet assassin and was given the alias: Winter Soldier. He was sent all across the globe, committing political assassinations with huge effects on the Cold War. However, his memory implantation caused mental instability, and he was kept in stasis between missions to prevent rebellion.

Captain America: The First Avenger
Portrayed by Sebastian Stan. Much like the comic, Bucky was Captain America's Sidekick. However during one the their missions, they were assign to capture Arnim Zola. During an attack with HYDRA Member, one of the members attempted to shoot Bucky. However the shot blew up hole in the train. Bucky ended up falling into the icy cold water below, and was declared legally dead.

Captain America: The Winter Soldier
The Winter Soldier appears as the titular secondary antagonist in the 2014 film Captain America: The Winter Soldier.  Stan reprised his role as James Buchanan "Bucky" Barnes, AKA, The Winter Soldier.

Powers and Skills
Because he was originally trained by Captain America, The Winter Solider is highly skilled on nearly all forms of hand-to-hand combat. He skilled on all kinds of firearms and bombs. He's a skilled knife thrower, and an expert marksman. His entire left arm has been mechanically modified, making it cybernetic(possibly made of vibranium). This has granted the Winter Soldier both superhuman strength and some other powers. Bucky was injected with the infinity formula, which has granted him semi-immortality, regenerative healing factor, and enhanced condition.