The Doctor and Bill in “Empress of Mars”

He's an Ice Warrior.

And they're the proper martians, right? They belong here?

Yes, the indigenous species. An ancient reptilian race. They built themselves a sort of bio-mechanical armour for protection. The creature within is at one with its carapace. The Ice Warriors. They could build a city under the sand yet drench the snows of Mars with innocent blood. They could slaughter whole civilisations, yet weep at the crushing of a flower.