Within
Marvel Comics, most tales take place within the fictional
Marvel Universe, which in turn is part of a larger
multiverse. Starting with issues of
Captain Britain, the main
continuity in which most Marvel storylines take place was designated
Earth-616, and the multiverse was established as being protected by
Merlyn. Each universe has a Captain Britain designated to protect its version of the British Isles. These protectors are collectively known as the
Captain Britain Corps. This numerical notation was continued in the series
Excalibur and other titles. Each universe of the Multiverse in Marvel also appears to be defended by a
Sorcerer Supreme at nearly all times, appointed by the mystic trinity of
Vishanti to defend the world against threats primarily magical in nature from within and beyond and bearing the
Eye of Agamotto.