Valis

Valis was a villain whose goal was to have "dominion over all things". He was a disembodied being, composed of gas-suspended carbon particles, and was highly flammable.

He captured the Doctor and Izzy after having stole the Crystal of consciousness. But the Doctor having swapped the crystal with an piece of perspex, Valis was defeated.

Two weeks later, he joined forces with several other alien to try and kill the Doctor, their common ennemy. He was later shot by Zargath who believed him to be the Doctor in disguise, and so exploding in the face of his murderer. (DW: Death to the Doctor!)