Ice Warrior

The Ice Warriors are a race of reptilian humanoids from Mars.

Physical characteristics
Ice Warriors have unknown facial features, since they have always been shown wearing their armour (though armour-less Ice Warriors have been seen outside of the TV series). They are humanoids with green skin and scales. They seem to have claw-like hands. They prefer cold climates and can be killed by extreme heat. Due to the differences in atmosphere and gravity, Ice Warriors seem to be perpetually wheezing and tend to move slowly.

Ice Warriors are almost always seen in their armour. They usually wear a green helmet with red eyes holes which covers everything but their mouths. The common Ice Warriors wear bulky green armour which looks like a thick shell, while the Ice Warrior lords wear light armour and capes.

History
The Ice Warriors inhabit a dying planet and have therefore tried to take over Earth for its resources. Their first attempt was in 2044 with a type of Martian fungus, which would turn the Earth into a more "liveable" planet (DW: The Seeds of Death). In the 3000s, several Ice Warriors trapped under a glacier tried to take over the scientific base (DW: The Ice Warriors). By the 3900s most of the Ice Warriors had renounced their war-like ways (DW: The Curse of Peladon).

Culture
Ice Warriors have a strong sense of honour. For example, in The Curse of Peladon, after the Doctor saved Izlyr's life, he felt that he had to try to help the Doctor escaped.

It is known that the Ice Warriors had an upper class at least until the 3900s.

Clans
Much of the Ice Warrior's early history/culture was defined by clans. The 1997 attempt at invading Earth (more specifically the United Kingdom) was by the Argyre Clan. (DW: The Dying Days)

It was another breakaway clan which formed the attack force which sought to invade Earth in 2044. (DW: The Seeds of Death)