Armus is a villain in the Star Trek universe that the Enterprise encountered on Vagra II in 2364. Armus was composed of a black viscous liquid that largely resembled an oil slick and was also a shape-shifter that could also assume a vaguely humanoid shape.
According to Armus, he was born of an unknown race that had left him on Vagra II. This race had purged from within them all the evil and negative attributes, which coalesced into a dank and vile second skin that was full of evil. The species abandoned Armus when they discovered what had happened.
In 2364 the crew of the Enterprise encountered Armus on Vagra II when a shuttle carrying Deanna Troi and a pilot crashed on the surface of the planet. The rescue team encountered Armus, who blocked their way to the shuttle. When Lieutenant Natasha Yar walked towards the shuttle, Armus responded with an energy attack that killed Yar within a matter of minutes.
Returning to the planet, the Enterprise away team tried to reason with Armus. Armus showed his total disregard for any other form of life, and dragged Commander Riker within itself.
Captain Picard traveled to the planet, at which point Armus released Commander Riker and allowed the away team to leave. Armus revealed his interest in leaving Varga II to find and punish the race that had abandoned him there. However Picard declared that he would not take Armus anywhere, and Armus became angry enough that his energy output slackened and the Enterprise was able to beam Picard and the occupants of the shuttle off the planet.
Following the return of the Enterprise crew to safety, the wreckage of the shuttle was destroyed with a photon torpedo in order to keep Armus from repairing the shuttle and leaving the planet. Picard then placed Varga II under a permanent quarantine, confining Armus on Varga II forever.