Valis was "high arbiter of the darkness". His goal was to have "dominion over all things". He was a disembodied being composed of gas-suspended carbon particles and was highly flammable.
Two weeks later, Valis joined forces with several aliens the Doctor had defeated before to try to kill the Doctor. He was shot by Zargath, who believed him the Doctor in disguise, and exploded in the face of his murderer. (COMIC: Death to the Doctor!)