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.