Gustave Lytton

Commander Lytton is a mercenary whom the Doctor encountered twice. He was born on a satellite called Riften 5, orbiting the planet Vita 15 some centuries in the future.

When the Fifth Doctor met Lytton he was working for the Daleks in a plot to rescue Davros from imprisonment following the events in Destiny of the Daleks. When Davros altered some of the Daleks to be loyal to him and tried to seize control from the Dalek Supreme, Lytton was one of the few survivors of the ensuing battle.

The Sixth Doctor then encountered Lytton planning to rob a diamond merchant. The sewers through which he planned to make his heist also contained a squad of Cybermen, and Lytton's actions helped revive them. After being taken to Telos with Lytton and the Cybermen, the Doctor encountered the Cryons, who revealed that Lytton was in fact working for them. The Cybermen had travelled back in time to prevent the destruction of their home planet Mondas in 1986. However, once they did so the Cybermen intended to destroy and leave Telos. Lytton's mission was to prevent this by stealing the time machine.

Once Lytton's treachery to the Cybermen was exposed, the Cyber Controller ordered that Lytton undergo the cyber-conversion process. When the Doctor tried to free Lytton from his fate as a Cyberman, a partially converted Lytton died fighting the Cyber Controller, who snapped his neck. The Doctor later admitted that he had badly misjudged Lytton.