Agents of STRIKE
MI-13 (also spelled MI:13 or MI13) is more formally called Deep Science Intelligence. It is a British extranormal espionage and response agency that dates back to World War II, predating both SHIELD and the SSR (something that MI-13 agents will not let you forget if you encounter them in the field).
It is the most experienced, most knowledgeable agency on extranormal affairs and works closely with SHIELD’s Academy of Technology and Sciences (which is based in Whitehall, the same city as MI-13’s headquarters).
MI-13’s recruitment program is rigorous, only bringing in the elite of the elites, and their operatives are to be respected when encountered. Their current chief, Brian Braddock, is a personal friend of Nick Fury.