The Nine was the main alias used by the ninth incarnation of a Renegade Time Lord who suffered from regenerative dissonance. This incarnation was notably known for his kleptomania, a trait noted both by himself (AUDIO: Companion Piece) and the Eighth Doctor. (AUDIO: Planet of the Ogrons)
Biography
The Crucible of Souls
After regenerating, the Nine initially claimed to be a new incarnation of the Doctor to Helen Sinclair and Liv Chenka. Rather than trying to be a "good man" like his predecessor, the Nine was motivated by kleptomanic greed. Helen and Liv helped him to rob the archive on Gallifrey, but he abandoned Liv when she became suspicious of his erratic and condescending behaviour. He took Helen hostage and brought her to the Crucible of Souls. He attempted to use the Crucible to gain immortality and exorcise his previous incarnations. After being thwarted by the Eighth Doctor, the Nine stole the Clocksmith's TARDIS and ran away. (AUDIO: The Crucible of Souls)
A collection of companions
While piloting the Clocksmith's TARDIS, the Nine ran into River Song, whom he kidnapped. He then decided to get a complete collection of the Doctor's companions, torturing River in order to find out their names and locations. After collecting them, they were placed in a prison. However, River was able to trick the Nine into gathering Liv, Helen, Charley and Bliss in one cell, before she manipulated the Nine into trying to acquire Katarina's corpse after River's own past self retrieved Katarina's body, River knowing that it would take time for the Nine to retrieve Katarina while playing on his ego to convince him to acquire a "rare" specimen for his collection. Using Liv's experience of technology, Helen's experience with codes, Bliss' knowledge of computer science, and Charley's nature as a temporal paradox, they were able to take control of the Nine's drones and escape their prison. Although the Nine returned with Katarina's corpse and nearly recaptured the women, his attempt to psychically link with Katarina's corpse to ascertain her identity caused Katarina's remaining mental activity to disrupt the Nine's own mental focus, allowing the women to defeat him. While River took the other companions home, Liv and Helen remained to be rescued by the Doctor, leaving the Nine in one of the cells in the prison. (AUDIO: Companion Piece)
The Ravenous
Still stuck at his own prison, he was caught by the Ravenous. Upon learning that the Ravenous couldn't eat him as his condition made his regenerative energy unappealing, the Nine attempted to use this information to set a trap for the Eighth Doctor, Liv and Helen. However, this trap was rejected by the Eleven as a foolish idea, as he perceived the Nine as having wasted such a useful opportunity to exploit his immunity to the Ravenous for a more long-term agenda. He disposed of his younger self by slipping a vortex manipulator onto his wrist and then activating it, sending the Nine to a random location in space and time. (AUDIO: The Odds Against)
Apocalypse Deathwatch
Tracking the Apocalypse Deathwatch - a ship that transported rich villains across the universe to observe mass catastrophes - the Nine attempted to steal most of the items on board, but acquired an unexpected ally in Thana, the last of a race who could only die from natural causes, who shared his interest in the rare. The Nine contemplated making her his "partner", but found himself facing a problem when the Deathwatch became caught up in a complex temporal rupture caused by the destruction of an ancient TARDIS. The situation became even more complicated for the Nine when he learned that the Fifth Doctor was also on the ship, along with a young woman who claimed to be the Doctor's daughter from the future.
The Nine initially claimed to be willing to help the Doctor get the Deathwatch out of the temporal rupture, but changed his plans when he realised that he could use the temporal ruptures to create a complex temporal network that would allow him to access all of Earth's history, as the fractured temporal splinters were actually fragments of a destroyed Earth. However, the Doctor was able to severe the temporal links the Nine had used to link his TARDIS to Earth, and then forced the Nine to retreat by threatening to time ram his vault. (AUDIO: Relative Time)
Legacy
When he was escaping from Gallifrey, the Eleven told the Nine that he didn't want him jeopardising his plans for the sake of his greed, after the Nine expressed his desire to steal the ancient artifacts of the Omega Vault. (AUDIO: The Eleven)
The Twelve used the Nine's expertise to break into a Dalek base. (AUDIO: Planet of the Ogrons)