Gustave Lytton, A galactic mercenary with the title of commander.  He was born on Riften 5, a satellite of Vita 15 (star system 690), known to be a planet of warriors. 

He first worked for the Daleks, commanding of a taskforce whose job it was to rescue Davros from his icy imprisonment in the  space penitentiary.  He fought the Fifth Doctor, and ultimately escaped through the Daleks’ time corridor to 1984 London (6P). 

There, with a small gang of petty thieves, he turned to organizing robberies to provide him with the money to buy sophisticated

electronics equipment, which he used to set upa transmitter broadcasting a distress call.  This was first picked up by the Cryons, and later by the Sixth Doctor. 

The Cryons hired Lytton to steal back a time vessel stolen by the Cybermen. Lytton met the Cybermen in the London sewers and pretended to help them in their mission, knocking Halley's Comet off course in 1985 and crashing it into earth preventing the future destruction of the Cybermen's original planet Mondas. 

Lytton then ends up on the Cybermen's new home planet Telos, where he is captured by the Cybermen, tortured, and forced to reveal his

and the Cryons plans.

The Cybermen decide to began the conversion work to turn him into one of their own.  Lytton before he lost his humanity, partially cybernised, manages to sacrifice himself to kill the Cybercontroller, before dying from injuries received (6T).