Wikipedia
S.H.I.E.L.D.
S.H.I.E.L.D. is a fictional espionage, law-enforcement, and counter-terrorism agency appearing in American comic books published by Marvel Comics. Created by Stan Lee and Jack Kirby in Strange Tales #135 (Aug. 1965), it often deals with paranormal and superhuman threats.
The acronym originally stood for Supreme Headquarters, International Espionage, Law-Enforcement Division. It was changed in 1991 to Strategic Hazard Intervention Espionage Logistics Directorate. Within the various films set in the Marvel Cinematic Universe, as well as multiple animated and live-action television series, the acronym stands for Strategic Homeland Intervention, Enforcement and Logistics Division.