The Secret Intelligence Service, commonly referred to as SIS or MI6 (Military Intelligence, Section 6), is the British intelligence organization focused on international affairs.
During World War II, Colonel Chester Phillips ordered Agent Peggy Carter to coordinate the SSR's work with MI6 so they could find the location of HYDRA Headquarters.
The Englishman was a former MI6 agent that went off the grid and was captured by Centipede Project and forced to work for them.
Rosalind Price was a member of MI6 using an alias before she became the leader of the Advanced Threat Containment Unit.
Uzman was a member of MI6 before he leaved and became a criminal. During his service at MI6, he created a special reagent which make people more suggestable and responsive.