The Devil Inside TV and Film

Sokar, "Stargate SG-1"

Bad boy, bad boy, whatcha gonna do?: Sokar, an ancient Goa'uld who once ruled the System Lord, posed as the god of death, even Satan, on many different worlds. He terraformed the moon Ne'tu, in orbit around his home world Delmak, into a literal version of hell to serve as a prison.

Scare Factor: A ten. The highest ranking. The being deliberately modified a moon's atmosphere, temperature, surface topography and ecology to be similar to those of Earth to make it habitable by humans, just so he could create hell. That's passion and dedication to a cause greater than Darth Vader's dark side.