Excrothian

The Excrothians were a species from the planet Excroth. Their civilisation was based on the principles of peace and enlightenment. When they started developing time travel, the Unon demanded the research to be stopped and destroyed the planet using a Dalek-made entropy engine when the Excrothians refused. The escaped survivors were forced to use robot-like walking tanks and started calling themselves Lect after the name of their ancient god of war and revenge. They were led by Grand Prelon Marleth.

The Ninth Doctor, Rose Tyler and Jack Harkness arrived in what should have been the Second Excrothian Tetrarchy, but found the planet was nothing but rocks. The Lect caught them, believing the reason the three time travellers were in the Excroth system may have been because they were working with the Unon. However, the three escaped when the Unon attacked one of their ships. Later on Fluren's World, the Lect came into conflict with the Unon, when the planet's emergency protocol caused the time bubble protecting the planet to vanish. Seeking to destroy the entropy engine, the Lect captured Rose and made her trick the Doctor into revealing the Unon's co-ordinates so she could get him out of the Unon's Perpetual City. The Unon then brought the Doctor on board the Lect command ship while they attacked the Perpetual City, suffering heavy losses. Using the Doctor's TARDIS to reach the entropy engine, Marleth turned the engine on itself, destroying it, and he and the Unon leader Arnora destroyed one another. (COMIC: Weapons of Past Destruction)