The (Captain Britain) Corps are a group of super heroes that exist in the Marvel multiverse. Their purpose is simple, keep the British Isles, and in extension the Earth safe.
They are often, but not always alternate versions of Captain Britain. Other persons that are members from different realities includes: Black Panther, Captain America, Ka-Zar, Killraven, Kymri, Lockheed, Meggan, Psylocke, Super-Skrull and Pete Wisdom.
The name varies, for instance - in Earth-616 they're commonly known as Captain Britain Corps, but on Earth-522 for example they would instead be known as Captain England Corps since the representative from Earth-522 is Captain England.
The Corps where originally formed by Merlyn, and there main priority was to protect the Marvel Multiverse. Each member of the squad would be set the task of protecting the dimensional equivalent of Britain. Even though they sometimes joined forces to defeat bigger and more dangerous foe.
Most recently the Corps, Excalibur and the Exiles fought Mad Jim Jaspers and the Fury. The Fury easily killed a great number of Captains, and afterwards Albion was appointed as their new leader. The Captain Britain Corps were destroyed during a conflict with the Mapmakers.