Earth Dimension(Also called the Mortal Plane and, for our purposes, the Marvel Universe.)Ruled By: No one. Doctor Strange is the Sorcerer Supreme.
This is the prime dimension of the Marvel Universe, the location of the vast majority of adventures in the Marvel Universe and in the MARVEL SUPER HEROES Role Playing Game. There appear to be more nexus points in Earth's dimension than in any other, and more dimensions and pocket-dimensions seem to intersect with the Earth dimension than any other.
Another peculiar facet of the dimension is the desire by so many different entities and factions to conquer and control it. It is quite possible that it is the nexus for all other dimensions, a type of hub in the wheel of the universes. Another possibility is that it is the largest of all dimensions, and yet contains fewer magical characters in proportion to its size.
The magic inherent in the Earth dimension seems to be of a different type than most other magical dimensions (the schools of "nature" magic and "white" magic being very strong). Furthermore, evil extra-dimensional beings, like Nightmare, Dormammu, Umar, and Tiboro have failed many times to conquer this dimension.
Astral projection within this dimension also seems easier than it does in others. Many forms of non-magical astral projection exist, particularly psionic and psychic abilities, but the projection is almost always confined within the Earth dimension. This may be because the astral plane runs through the entire dimension, instead of only intersecting it in places.
The Earth dimension of the Marvel Universe was created by the Big Bang, that is, the explosion of primal mass at the center of the universe flung particles throughout the dimension which eventually formed the planets, stars, and everything else.
It is known that before the age of man, Shuma-Gorath, "Him Who Sleeps But Who Will Awaken", ruled all. Outwitted by an opponent, Shuma-Gorath left to sleep the sleep of eons. Occasionally, every millennium, he can try to return to reclaim his dimension, but has been recently prevented from doing this by Doctor Strange.