The Servants of the Mushroom Cloud are a religious organization led by Charmaine, that worships the nuclear holocaust as a holy event and nuclear energy as divine. They occupy the Las Vegas Nuclear Power Plant, maintaining it and providing electricity to the city (and possibly other outlying settlements). They are seeking to convert everyone in the wastes to their "poisonous religion", as Faran Brygo puts it.
The Servants believe in the Great Glow that guides them (radiation) and worship Einstein, who gave the theory, and Oppenheimer, who gave the bomb. All members are singlemindedly focused on furthering the cause of the Mushroom Cloud and converting people in the wastes to follow them.
Apart from human worshippers, the Servants also benefit from the services of Temple Guardians, blue-robed half-humans mutated by radiation poisoning that can make short work of any infidels... provided they're not Rangers, of course. The most beautiful and bizarre of members are Radiation Angels, beings seemingly composed of nothing but radioactive dust.