Ice Warriors are native Martians. They were huge, green, scaly creatures, equipped with sonic guns (on their claws) and heavy Armour.  Coming from a super-cold environment, the Ice Warriors were sensitive to heat, which was their only known weakness.  The leaders appeared to be slightly sleeker and less bulky than the warriors. 

The Martians scouted Earth during its first Ice Age.  A squadron led by Varga was accidentally trapped and frozen in ice.  Soon afterwards, possibly because they had not heard from Varga, the Martians decided to leave their dying planet and emigrate to another world in the galaxy (OO)

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The Second Doctor first came across the Martians when Varga and his men were found buried in a glacier in 3000 AD.  The name "Ice Warrior" was originally coined by Walters, but it was apparently close to the original Martian term, since they also referred to themselves by that name. 

The Doctor foiled Varga’s attempts at conquest and destroyed the Ice Warriors and their ship (OO).  The Second Doctor met the Martians again when, towards the end of the 21^st Century, a war-like party of Ice Warriors, under Slaar’s leadership, returned to the Solar System and tried to conquer Earth by using the so-called "Seeds of Death".

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Slaar’s defeat seemed to have convinced the other Martians to abandon any further attempts at attacking the Solar System (XX).  The Martians then built a small, presumably peaceful, empire of their own, and eventually joined the Federation. 

Their ambassador to Peladon, Izlyr, helped the Third Doctor thwart Arcturus’s plans (MMM).  A renegade Ice Warrior, Azaxyr, later betrayed the Federation to Galaxy 5 on Peladon, but was foiled by the Third Doctor (YYY).