Ice Warriors

"Believe me, I know the Ice Warriors, Jo. They're a savage and a warlike race."

Described by the Tenth Doctor as "a fine and noble race who built an empire out of snow", the Ice Warriors were a species of reptiles from the planet Mars. They were twice encountered by the Second Doctor – first, when their crashed ship was thawed out of a glacier during a future Earth ice age, and then when they tried to take over the Earth’s trans-mat system. On both occasions, the Warriors were dangerous aggressors. In a subsequent meeting with the Third Doctor on Peladon, the Ice Warriors had renounced violence and entered the Galactic Federation.

Many years later, the Eleventh Doctor and Clara met sole Ice Warrior Skaldak aboard a Russian submarine, the Firebird, on Earth in the Eighties whilst the rest of his race were scattered across the universe (including one hidden in a Trap Street in London). The Twelfth Doctor and Bill met Ice Queen Iraxxa on Mars in 1881 which led to contact with Alpha Centauri and the dawning of the Martian Golden Age.