The Magic domain was claimed by Veros when he learned to manipulate existence. It was then split and acquired by Chactross.
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The Magic Domain includes the Arcane Power sources and indicates that the holder of that domain controls and influences the ebb and flow of the energy that courses through the universe. Often creatures created by such a god have an affinity for magic.
Wizards and any seeking power worship the god who holds this domain, in hopes that the subtleties of the art will be revealed to them.
Because of Chactross's demands on Veros, magic has been effectively split into two domains. One is the power of controlled magic, that of Wizards, ritual spellcasters, certain warlocks, as well as many intelligent magical creatures. The other magic is wild and untamed, and is used by Sorcerers, warlocks, and other creatures. It is this "wild magic" which allows a blink dog to teleport, for example.