The Saurians were an advanced reptilian species from the galactic centre. They were humanoid with long heads and tusks, silver scales, huge purple eyes and a musky odour. They reproduced by laying large blue eggs.
The Saurians, desiring to conquer the galaxy, began attacking other worlds with their cosmic rays, encountering little resistance until Earth became involved. At that point, humanity had developed the ability to pilot their world through space, and also to turn it invisible. For centuries, the Saurians unsuccessfully attempted to ward off Earth's attacks.
After the Saurians devastated one planet during the war, they detected the arrival of the Second Doctor, Jamie and Victoria in the TARDIS and captured them. Their leader, Lord Haxtl, planned to have them dissected to discover the secrets he believed they possessed. The Doctor convinced him that he would help defeat Earth if he would allow them access to the TARDIS, claiming that it held the secrets he wanted. After entering the ship, they departed. (PROSE: Lords of the Galaxy)