You know those moments when you’re somewhere unfamiliar, and you get the distinct feeling you’re being watched… only when you turn round, there’s just a blue, gaseous cloud floating around waiting for you to die so it can steal your corpse and go terrify a famous author?
This lot do… The Gelth.
The periodic table’s version of the Puss in Boots character off of the Shrek films, this species’ cunning strategy is to make humans feel sorry for them by reanimating their dead relatives and using them to snap their necks (presumably a traditional greeting within their society) and then immediately go all flamey and badass on them.
Aside from that, we don’t know a great deal about them. They once had bodies, lost them in the Time War (very careless, I know) and were converted to gas-forms. Somehow they then discovered the rift, which had opened at a funeral parlour in Cardiff. The gaseous nature of the rift kept them alive, and from this position they were able to dominate the heating and lighting industries of the late 19th Century.
It is thought that their domination of the Cardiff power network led directly to the formation of British Gas (thus explaining their blue flame logo).
But Gelth are also able to survive in the otherwise inhospitable (and unthinkable) conditions of a human corpse, thanks to the gasses produced by a body in decay. They then reanimate the bodies and go out to the theatre, or try and kill a stranger – just like any other friendly neighbourhood joyrider.
During his one encounter with this species, the Ninth Doctor offered to help them find a planet of their own until he realised their deceit and their actual intention to take control of the planet by force. They were defeated by the servant of the funeral parlour’s owner, who just happened to have psychic abilities and the knowledge of how to close a rift in time and space. When the rift was closed on the invading creatures, the remaining Gelth were destroyed by fire. The servant died and then became a key member of Torchwood…
First appearance: The Unquiet Dead (2005)
Sworn enemy: Neon, Argon, Mercury vapour. You know, any of the show-offy fluorescent ones.
Strengths: Gaseous form – can enter spaces undetected.
Weaknesses: Strong gusts of wind, naked flames…