Yana

Professor Yana was a Human identity the Master created for himself when he used a Chameleon Arch to escape the Last Great Time War.

Origins

 * The circumstances of the transformation of the Master from Time Lord into Yana remain unknown, though, as he had the same kind of fob watch, he had presumably used a chameleon arch as the Doctor had done to change himself into John Smith.
 * The name Yana was an acronym of "You Are Not Alone", which had been the Face of Boe's dying words to the Doctor. (DW: Gridlock)

During the Last Great Time War, the Master was resurrected by the Time Lords and was assigned to protecting the Cruciform from the Daleks. He failed his task and became scared, so scared that he ran from the war to the end of the universe and used a chameleon arch to become Human.

Just as John Smith had false memories concerning his early life, Yana might have false memories created when Yana came to existence. It can be said with some degree of certainty that at least seventeen years of Yana's memories prior to meeting the Doctor were real, as that is how long he had been with Chantho.

Physically Human, Yana was an orphan found on the coast of the Silver Devastation with only a "heirloom" fob watch. He could never keep time and was always late for things. He spent his life moving from one refugee ship to another and all his life he heard the sound of drums every waking hour as if they were getting closer.
 * The Master had heard this drumbeat ever since he had stared in the Untempered Schism as a boy. (DW: The Sound of Drums)

Career as scientist
Yana retained the Master's brilliant intellect and ultimately became responsible for sending the remnants of Humanity to Utopia. He eventually became friends with another scientist Chantho, who was thought to be the last of the Malmooth race. Together, they worked on the Utopia Project to convey the surviving Humans from the planet Malcassairo to Utopia.

Meeting the Doctor
Yana met the Doctor, Jack Harkness, and Martha Jones, who said phrases curiously familiar to him, phrases such as Time Vortex, "extermination", Time War, Daleks and regeneration. Martha made the Professor suspicious of a watch in his possession, so that, hearing voices in his mind that commanded and entreated him, he activated the device and returned to his true identity.

Personality
In his human form, Yana was a benign old man who had nevertheless lost some faith in the Utopia project. His spirit was revitalised by the Doctor, and the two shared a mutual admiration. He was also somewhat scatterbrained and slightly lacking in self-confidence, at one point referring to himself as "a stupid old man." (DW: Utopia)