Black Widow
This character made her debut in the Marvel Universe with Iron Man 2, only to become one of the main characters of the Avengers’ group. Scarlett Johansson brought Natasha Romanoff to the big screen and her performance became so renowned that Marvel is already working on her standalone sequel to be released in 2020. Look how she has changed in the last 10 years.
S.H.I.E.L.D. stands for Strategic Homeland Intervention, Enforcement, and Logistics Division,
not "Supreme Headquarters, International Espionage, Law-Enforcement Division" as is claimed here. Get it right, man...