Vagra II natives were "a race of Titans" who were formerly native of the planetVagra II, who departed the planet "a very long time [ago]."
This race was said to have "perfected a means of bringing to the surface all that was evil and negative within," so that they would free their "bonds of destructiveness."
As these emotions came to to the surface, it formed into an entity, a "second skin, dank and vile" – a "skin of evil" identified only as Armus. What remained was then discarded on Vagra II, left alone and rejected by those who created it, where it suffered for eternity, festering in its own anger.
Those that departed Vagra II were later described by Armus as "creatures whose beauty now dazzles all who see them." (TNG: "Skin of Evil")
This species was only mentioned in dialogue.
According to the Star Trek Encyclopedia (4th ed., vol. 1, p. 45), Armus was created by the Vagrans, a species native to Vagra II.