Tyranid
OMNOMNOMNOMNOMNOMNOM Delicious Biomass, you must devour it
"Tyranids" are extragalactic beings in Warhammer 40k that exist only to eat living thngs. They have been expected to arrive on Terra's doorstep anyday now for years, being stalled by a force even more malicious then they are: GW's reluctance to move the story forward.