L is for... L3

The L3 robot was also known as Drathro. It had been created by Andromedans and sent to Earth to supervise a subterranean shelter where a group of Andromedans were being held in suspended animation, awaiting a rescue mission. They had stolen a large amount of top secret material from the Matrix on Gallifrey. 

The Time Lords discovered this and decided to destroy the Earth in order to prevent the secrets reaching Andromeda. The planet was moved through space, causing a fireball which destroyed most of the surface. When the rescue mission arrived, the planet was gone. The "sleepers" eventually died.

With no new orders Drathro continued to run the shelter, however. It believed itself far superior to the organics who lived in the shelter.

It maintained a fixed population, ordering culls when numbers exceeded 500. It employed some humans, known as Train Guards as the shelter had once been a London Underground station, to police the shelter whilst it never left its inner control area. It took two of the brightest humans - young men named Humker and Tandrell - to work for it in the control room.

It could kill with electric shocks from its hands, and controlled a tank-like L1 service robot to carry out tasks beyond the station.

The captain of the Train Guards - Merdeen - was secretly freeing some of the station inhabitants and they had joined the Tribe of the Free on the surface. Its ruler, Queen Katryca, knew Drathro as "the Immortal", and planned to destroy it. The tribe had a totem pole which they worshipped, unaware that it was actually the source of Drathros' power - a black light converter.

The Master sent a mercenary named Glitz, along with his companion Dibber, to steal the Matrix secrets. Dibber sabotaged the station by blowing up the converter. The Doctor was horrified by this as no-one knew what would happen if a device like this exploded. As he attempted to stop the blast, Glitz fooled Drathro into accompanying him to his spaceship where he claimed he had more black light. 

Away from his control centre, Drathro collapsed and melted.

Operated by: Paul McGuiness. Voiced by: Roger Brierley. Appearances: Trial of a Time Lord Parts 1 - 4 (1986).

• Actor Roger Brierley was supposed to operate the L3 as well as provide the voice, but his claustrophobia prevented him doing so. The VFX team had anticipated this and it had been built using McGuiness as a model, as he was of similar build to Brierley.
• This story, which is also known as The Mysterious Planet, was the last completed work by writer Robert Holmes. He borrowed elements of his very first story - The Krotons - for it.