- "An object of unknown origin. Kind of like you. Team goes in, determines if it's useful or if it poses a threat. Last one turned out to be pretty interesting."
- ―Phil Coulson[src]
0-8-4 is a fictional government classification featured in the Marvel Cinematic Universe, which is based on properties created and developed by Marvel Comics. It is a designation used by the espionage agency known as S.H.I.E.L.D. and refers to objects of unknown origin. It was first used in 2010 when agents of S.H.I.E.L.D. discovered the hammer of Thor in the deserts of New Mexico. 
Since 2012, following the Battle of New York, many items that fall under the 0-8-4 code relate to alien technology developed by the Chitauri and fueled by tesseract energy, such as Item 47, which was investigated by Jasper Sitwell. 
In 2013, a special S.H.I.E.L.D. response team were sent to the jungles of Peru where they discovered a piece of technology that had been embedded in the wall of a pyramid ever since the 1940s. The team determined that the item may have been built by HYDRA during World War II and it was powered by a fuel cell comprised of both tesseract energy and gamma radiation. The team recovered the device, but a Policía Militar de Perú unit tried to steal it from them aboard the S.H.I.E.L.D. mobile command center en route back to the United States. The device activated, crippling the aircraft. S.H.I.E.L.D. agents defeated the enemy soldiers and secured the device. After which, Agent Phil Coulson determined that it was too dangerous to exist, and they initiated their slingshot protocol, which involved placing the item aboard a rocket drone and firing it into the sun.