Zargath

Zargath was a villain who tried to invade Powell Estate. His Imperial Militia has been there for only five minutes when the Doctor, helped by Rose, used his sonic screwdriver to make it rain. Zargath's people being allegic to water, they were quickly defeated.

Some time later, Zargath joined forces with other aliens to try to kill the Doctor, their common enemy. He shot Valis, believing him the Doctor in disguise. Being a highly flammable gaseous alien, Valis exploded, blowing Zargath to smithereens. (DW: Death to the Doctor!)