KGB

"When I first joined S.H.I.E.L.D., I thought it was going straight. But I guess I just traded in the KGB for HYDRA."

- Black Widow

KGB, the Komitet gosudarstvennoy bezopasnosti (Russian: Комитет государственной безопасности, translated in English as Committee for State Security), was the main security agency for the Soviet Union until its collapse.

History
At some point in her life, Natasha Romanoff was recruited into the KGB. As a KGB operative, she was assigned to escort an Iranian nuclear engineer in Odessa, Ukraine, when they were attacked by the HYDRA operative Bucky Barnes. Romanoff attempted to protect the engineer but Barnes shot through her stomach and killed the engineer. This incident gave Barnes the name Winter Soldier.