Following the end of World War II in May 1945, over 1,500 German scientists, engineers, and technicians were recruited by the United States in a classified effort known as "Operation Paperclip". Chief among them was former HYDRA scientist Arnim Zola, who joined S.H.I.E.L.D. in a clandestine attempt to rebuild HYDRA from inside the newly-founded peacekeeping organization.
In 1991, HYDRA learned that S.H.I.E.L.D. co-founder Howard Stark had recreated the Super Soldier Serum and tasked Vasily Karpov, a sleeper agent embedded in the Russian Armed Forces, with reviving the Winter Soldier. Karpov did as he was told, ordering the master assassin to retrieve the serum and leave no witnesses behind.
- "Help... my wife... help my wife. Sergeant Barnes?"
- ―Howard Stark's last words
As the Winter Soldier approached the fallen vehicle, Stark crawled from the car and asked him to help Maria. He recognized the assassin as Bucky Barnes only to be repeatedly punched in the face and have his skull crushed by the Soldier's cybernetic arm.
After placing Stark's corpse back inside the car and strangling Maria to death, the Soldier proceeded to shoot at a nearby security camera before departing with the serum.
- "I never got to say goodbye to my father."
- ―Tony Stark
The newspapers reported on the Starks' passing, but their deaths were attributed to a simple car accident. Steve Rogers later learned the Starks' deaths had been perpetrated by HYDRA from Arnim Zola, but was unaware Bucky was the assassin.
HYDRA used the serum to give five individuals the same capabilities as the Winter Soldier, but they proved too dangerous to be sent into the field and remained in suspended animation at a facility in Siberia.
In chronological order:
- Captain America: Civil War (flashback)
- Iron Man (mentioned as a car accident)
- Iron Man 2 (mentioned as a car accident)
- Captain America: The Winter Soldier (mentioned as an assassination by Winter Soldier; shown via HYDRA footage)
- Captain America: Civil War (shown via HYDRA footage)
- Avengers: Infinity War Prelude (shown via HYDRA footage)