Gustave Lytton

Commander Gustave Lytton was a mercenary who, at different times, worked for the Daleks and later for the Cryons.

Biography
Lytton was born on the satellite Riften 5, orbiting the planet Vita 15. He knew of the Time Lords. (DW: Attack of the Cybermen)

When the Doctor first encountered Lytton, he was leading a squad of Dalek Troopers in a plot to rescue Davros from imprisonment in stasis on a Human prison space station. When Davros altered some of the Daleks to be loyal to him and attempted to seize control from the Dalek Supreme, Lytton was one of the few survivors of the ensuing battle and was left trapped in London in the year 1984. (DW: Resurrection of the Daleks)

Consequently, Cryon resistance fighters contacted him. With Cryon planet, Telos, occupied by Cybermen, they sought help from him in freeing themselves. Lytton assembled underworld contacts in appeared a plot order to rob a diamond merchant. He actually planned on contacting the Cybermen living in the London sewers in order to win the trust of the Cybermen, so that he could betray them on behalf of the Cryons.

Lytton met the Sixth Doctor, once again, who recognized him from their previous encounter. The Doctor distrusted him immediately, even after the Cybermen took Lytton prisoner as well. The Cybermen transported Lytton, along with the Doctor and his companion, Peri to Telos, where it was revealed to the Doctor that Lytton was working for the Cryons and not for the Cybermen themselves.

Once Lytton's treachery to the Cybermen was conclusively proven to the Cybermen, the Cyber-Controller ordered that Lytton undergo the cyber-conversion process. The Doctor tried to free Lytton from his fate as a Cyberman, a partially converted Lytton died fighting the Cyber-Controller. (DW: Attack of the Cybermen)

Personality
Lytton's people were known as mercenaries, rarely doing anything if there wasn't money attached. Lytton was no differen't, he berated his men and threatened potential muttineers with death. He contantly insulted the intelligence of those under him and was willing to sell them out to the cybermen in exchange for his life. However his decision to help the Cryons overthrow the cybermen caused the Doctor to admit that he had badly misjudged Lytton and his intentions. (DW: Attack of the Cybermen)

Behind the scenes

 * Lytton's full name wasn't given in his television appearances. His first name comes from the Target Books novelisation Attack of the Cybermen. It was reused in the Doctor Who Magazine story Mistaken Identity.