Yana
One more lost soul dreaming of Utopia.
Professor Yana appeared to be a Human scientist, who was in reality an incarnation of the renegade Time Lord known as the Master.
Profile
Just as John Smith had false memories concerning his early life, Yana's might have remembered false memories created when Yana came to existence. It can be said with some degree of certainty that at least 17 years of Yana's memories prior to meeting the Doctor are 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 fob watch, which in reality held the Time Lord self of the Master. 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.
In actuality, as the Doctor had done, he had subsumed his identity into that of a human form and locked his actual Time Lord identity into the fob watch. As the Master later observed, this disguise was so perfect that he forgot who he was, although Yana was plagued by half-remembered fragments of his former life (a fallout of the fob watch) and terrible headaches in which he heard the beat of drums (which had been harassing the Master's mind since he stared directly at the Time Vortex, at Gallifrey). Yana retained the Master's brilliant intellect and ultimately became responsible for sending the remnants of Humanity to Utopia.
He eventually became friends with the last of Malmooth race, scientist Chantho, thought to be the last of her kind. Together, they worked on the Utopia Project to get the humans from the planet Malcassairo to Utopia.
Yana met the Doctor and Martha Jones who said phrases curiously familiar to him, phrases such as Time Vortex, Time War 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.
As the Master, he let down the defences allowing the Futurekind in and dismantled the components, which allowed the system for the rocket to start up in the first place. Chantho held him at gunpoint. The Master grabbed the loose end of the live electrical cable and first threatened and then fatally attacked her, incidentally killing the last of the Malmooth.
As the Master grabbed the Doctor's hand, which Jack Harkness had brought to Malcassario, the dying Chantho managed to shoot him before she died herself. The Master stumbled into the Doctor's TARDIS with the hand, locked the door with a deadlock seal and regenerated.
The name Yana is thought to be an acronym of "You Are Not Alone", a reference to the Face of Boe's dying words.
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."
After his Time Lord essence was restored, the Master reverted to his usual self, sexist, arrogant and ruthless with a cold dignity. All traces of the benevolent and humble Professor Yana were flushed away and replaced with a vindictive sense of humour and a bitter, vicious streak, sharpened by his sense of humiliation at having spent years as a human, a being he sees as degenerate.
