The L1 was a service robot used by Drathro in Marb Station on 2,000,000 Ravalox. The robot was tank-like and equipped with a camera, search light, tentacles, and a tracer disc. It could climb up stairs on its treads, stun with electricity, and it was capable of crashing through rock walls.
L1 was sent to capture the Sixth Doctor and bring him back to the station to repair the black light converter that powered Drathro and the station. While trying to bring him back, however, the L1 was ambushed by Katryca and her warriors who, thinking it was the Immortal (meaning Drathro), destroyed it with their guns. (TV: The Mysterious Planet)