Sleeper (The Mysterious Planet)

The Sleepers was the name used for three presumed humanoids from Andromeda who found a way into the the Matrix five hundred years before the Doctor arrived on Ravolox. When they fled to Earth, the Time Lords devastated it with a fire ball. The three were able to escape the Time Lord's establishing and hiding in an underground bunker. They also created the L3 robot that would later be known as Drathro to maintain the bunker while the three sleepers put themselves in suspended animation, both of which were powered by a black light power system. A few later prior to the Doctor's arrival, the system began to break down, which Drathro was unable to correct because he was trained in installation and maintenance. As a result the three sleepers died whilst in suspended animation. (DW: The Mysterious Planet)