Cyber-Lieutenant (Earthshock)

A Cyber-Lieutenant served under a Cyber-Leader in a CyberNeomorph plot to destroy Earth in 2526 to prevent an alliance forming to destroy the Cybermen. Based on Briggs' freighter, they planned to use a Cyber-bomb to destroy Earth. However, the bomb failed due to the Fifth Doctor's intervention.

After the bomb failed, the Cybermen began a second plan to destroy Earth, involving them reawakening an army of Cybermen stowing away in Briggs' freighter, taking over the ship, and crashing it into Earth. The Lieutenant was in charge of reawakening the Cyberman army hiding on Briggs' freighter.

Eventually, after the freighter was set to crash into Earth, the Cyber-Leader decided to use the Doctor's TARDIS to escape the ship, with the Cyber-Lieutenant accompanying him. While the Lieutenant was searching the rest of the TARDIS, the Doctor killed the Cyber-Leader with Adric's gold badge and the Leader's Cyber-gun. When the Cyber-Lieutenant returned to the TARDIS control room, Nyssa also used the dead Cyber-Leader's Cyber-gun to kill the Lieutenant before it could kill the Doctor. (TV: Earthshock)

Behind the scenes
This Cyber-Lieutenant was the first of its kind to enter the Doctor's TARDIS.