The Ice Warriors were a race of reptilian humanoids from Mars.
Physical characteristics
Ice Warriors were large, imposing reptilian humanoids, reaching up to 7 feet tall. They had unknown facial features, since they always wore their armour. Their tongues were thin and green. (BNA: The Medusa Effect) They had claw-like hands. They preferred cold climates and could be killed by extreme heat. Due to the differences in atmosphere and gravity, Ice Warriors seem to be perpetually wheezing and tended to move slowly. (DW: The Seeds of Death)
Technology
Ice Warriors almost always wore thick, green, ceremonial armour. They usually wore a green helmet with a red blast-screen which covered everything but their mouths. The common Ice Warriors wore bulky green armour which looked like a thick shell, while the Ice Warrior lords wore light armour and capes. By the late 26th century, this armour was built directly into the body. (BNA: The Medusa Effect)
This armour was controlled by an implant at the back of the brain and powered by the Ice Warrior's nervous system. Ice Warriors also had artificial membranes inside their throats, allowing them to filter out the necessary gases for survival. (BNA: The Medusa Effect)
History
The Ice Warriors inhabit a dying planet and have therefore tried to take over Earth for its resources.
The Ice Warriors made their first attempt to invade Earth in 1997, specifically the United Kingdoms. (DW: The Dying Days) The next invasion was in 2044, when they attempted to use a type of Martian fungus, which would turn the Earth into a more "liveable" planet. (DW: The Seeds of Death)
In 2086, another invasion was attempted, leading to the Thousand Day War. By 2088, the Humans had won this conflict. (NA: GodEngine, The Dying Days) By the 22nd century, the Ice Warriors had become allies with the Humans. These Ice Warriors came into conflict with the Selachian Empire when one colony refused to sell weapons to the Ockorans. The Ockorans used their sun-stoker on these colonists, killing them. (PDA: The Final Sanction)
In the 31st century, several Ice Warriors trapped under a glacier tried to take over a scientific base (DW: The Ice Warriors). By the 40th century 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, after the Doctor saved Izlyr's life, he felt that he had to try to help the Doctor escaped. (DW: The Curse of Peladon) They also believed that in the case of a violent death, the victim will not rest in peace until the murderer has atoned for it. (BNA: The Medusa Effect)
It is known that the Ice Warriors had an upper class at least until the late 40th century. (DW: The Curse of Peladon)
Ice Warriors were not known for their sense of humour. (BNA: The Medusa Effect)
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)