Circle of the Scarlet Moon
All information presented here is from Champions Universe, 6th ed., page 128.
For all things there must be a balance - any competent mystic will tell you so. Just as the forces of Light have the Trismegistus Council to aid them, the forces of Darkness know the cold comforts of alliance with the Circle of the Scarlet Moon.
Though in truth, it was the Circle that came first, not the Council. Some in the Circle are said to trace the organization's roots back as far as certain blasphemous witch-covens in medieval Germany, but the only thing anyone can say for sure is that a French noble, Viscomte Gildas de Valenois, founded the Circle as a formal coven in 1783. The Viscomte recruited other dissolute members of the French aristocracy, eager for both power and perverse pleasures, to study black magic with him. Though their "powers" didn't save most of them from the guillotine during the French Revolution, enough escaped to continue the Circle. Some say the ghost of de Valenois, carrying his severed head in his left hand, escorted most of the survivors to safety in the new land of America.
Settling in the former British colonies, the members of the Circle resumed their practice of Dark Arts, only to find they had acquired an enemy - the Trismegistus Council, which sought to thwart their diabolic schemes. Aided, the Circle believes, by other forces of Light, the Council defeated the Circle far more often than the Circle triumphed over it.
Rumor in the Mystic World has it that shortly after the turn of the twentieth century, the Circle worked a might spell to overcome its greatest enemy once and for all, but the spell failed, leaving the Circle badly weakened. Since then the organization has remained in the shadows, carefully hoarding its strength and hatching only the most secretive of plots and schemes. Toady, strengthened by many new and powerful members, it's once again poised to resume its quest for occult power.
Want to know more? Pick up CU6ed, Champions Villains Vol. 2 and Mystic World, 5th ed. All of them have more information on the Scarlet Moon.