The Master

The Master is a rogue Time Lord that is the doctors friend "well sometimes"

The Master went to the academy with The Original Doctor. They were the best of friends until he killed The Doctor's mother. Ultimately,that resulted in the end of his friendship with The Doctor. soon the master saw his old friend steal a Type 40 TARDIS and did the same thing and stool a TARDIS. Not much is Know about the master's solo adventures but At one point, The Master kidnaps and tortures The Devious Doctor, reavealing The Doctor's criminal status to him. Due to this, The Doctor try's to strangle The Master to death due to his anger-but the master escapes the crime scene before the Time Lords take the doctor to the execution room on Gallifray. When the master's plan of the doctor being dead was ready the Doctors companion Gen framed The Master for killer and was exiled to earth but before he left he electrocuted the doctor and was sent to earth.The Master spent his time stuck on Earth through the 1970s right through to 1997 when the Doctor and Gen came to visit Earth .He worked for the United Nations and then defected to China after being sent there to assist against alien parasites. He turned the parasites into a way of brainwashing political prisoners into zombie-like soldiers organised into Ke Le Divisions.
 * early life
 * Travels alone and facing the doctor again
 * framed and exiled to earth

Losing favour with the new Chinese government in 1997, the Master built a teleport device that helped him find his TARDIS and was able to travel in time and space again.