GHI

G

Gelth
Home Planet: Unknown
Life Form: Gaseous lifeform
Info: The Gelth were intelligent gaseous lifeforms who claimed to have lost their corporeal forms due to the Time War. They traveled through a rift and, via gas in decomposing bodies, they took possession of the recently deceased.

They claimed they were on the verge of extinction, and convinced the Doctor to help them through into our plane of existence via Gwyneth. However, instead they took possession of more corpses and intended to take the Earth by force.

They were ultimately killed in an explosion, however its unknown whether all Gelth actually perished.
Episodes appeared: The Unquiet Dead


Graske
Home Planet: Griffoth
Life Form: Changeling
Info: Known to be able to transmat through time and space, the Graske often abduct individuals and replacing them with their own kind. To see them you have to detect a mysterious green glow in their eyes.


In the SJA, a Graske appeared as a servant of the Trickster. Considering the nature of how they live their lives - replacing people and living of their lifespan/energy it could be suggested that the Graske forms part of the Tricksters Brigade
Episodes appeared: Attack of the Graske


H


Hath
Home Planet: Messaline
Life Form: Humanoid Fish
Info:They are intelligent, emotional creatures and are fully sentient, although there language takes a while to understand due to it begin relayed through a bubbling liquid.

One of the most referred to Hath, is Peck, who befriended Martha and helped her across the planet's surface. He ended up sacrificing himself and suffocating in a muddy swamp, to save Martha.
Episode appeared: The Doctor's Daughter


Hoix
Home Planet: Unknown
Life Form: Exo-skeletal alien
Info: The Hoix are a race of exo-skeletal aliens, which a very bad and vicious attitude, and who only live to eat, no matter what else. Since they just appeared on Earth, and behave similarly to a Weevil , it could be suggested they are from the same homeworld, or are a similar species.


They appear to have an aversion to warm liquids, any contact with them with most likely disable them. However, if attacked with cold liquid they will only become enraged. If you have some food (preferably meat) they will become easily distracted.
Episode appeared: Love and Monsters, Exit Wounds (Torchwood)


The Hosts
Home Planet: Sto
Life Form: Information Droid
Info: The Hosts were created by Max Capricorn to provide information and assistance to people on board the Spaceship Titanic. They are programed to simply obey the highest person of authority and will do so without hesitation or emotion.


They are not only incredibly powerful - having the strength of ten men - but they can also use to wings to levitate and their halos as powerful, and deadly, weapons. One way to outwit an attacking Host is to use Emergency program 1, which grants you three questions.
Episode appeared: Voyage of the Damned


I


Isolus
Home Planet: The Sun
Life Form: Vegetation
Info: The Isolus exist in a family of millions, traveling in seed pods across space and keeping themselves amused by playing games via their immense imaginations. They are essentially children, only becoming adult after hundreds of years.


Because of the Isolus' immense brain, it has the ability to trap people within their own worlds. When a single Isolus becomes merged with a child, this other world is glimpsed through their drawings. The Isolus needs a form of energy to be able to power their pods, such as heat, or even a powerful emotion.
Episode appeared: Fear Her


(Fourth part continued here: J-L)