The Professor

The Professor was a Time Lord, and a contemporary of The Doctor. Little is known about him now, as the only record of him left is a hologram that remains as the 'autopilot' and guardian of his TARDIS, made as a complete 'mental upload copy' of him in the late 1980s. As such, the hologram's memories stop there, so everything that happened to the actual Time Lord after that is unknown.

Since the Time Lord Professor is presumed dead, along with every other Time Lord aside from The Doctor, the hologram in his image is thought of as The Professor now, posessing a fully sapient and free-thinking artificial intelligence.
 * This article covers what is known about the flesh-and-blood Professor, as well as the hologram's activities since the Five discovered him.

Early Life
As a boy and young man, The Professor attended the Prydonian Academy alongside The Doctor, a classmate in many of the same subjects. The two had a casual friendship, though both were members of The Deca, a clique of academy students known for their rebellious behaviour but outstanding abilities. As 'young men', the two began to have divergent opinions and philosophies as to their craft, and maintained more of a professional, if a bit cold, relationship.

As a boy, he was brought to the Untempered Schism like all Time Lord candidates. He later told the Five that, "it made me feel small. It really did make me feel my place in the universe.  I was scared, sad... but also awed."

Little else is known about his early life, though the Doctor had this to say about him when he was mentioned: "He needs to get out of his laboratory and out of his classroom and actually live history. You can't accomplish everything inside some lab, you must feel the worlds beneath your feet!"

Life as a Time Lord
As with much of his life, little is known about the bulk of his service as a Time Lord. Apparently some time after The Doctor's exile from Gallifrey, The Professor actually did go out and start exploring the cosmos. He visited many places, so much so that he actually began to collect trophies from his adventures. Among these relics were a Glittergun (suggesting that he had fought Cybermen), a Terraforming Glove, a mobile emitter for holograms, and the Chest of Dreams, which had (supposedly) once contained a "demon".

The Professor's Companion
Sometime in his journeys he came into the company of a young woman named Zoe. Her exact race is unknown, but she is supposed to be human, as her appearance is such. She had her own bedroom on the TARDIS, which she decorated in a soft, feminine way that was a starker conttrast to the rest of the ship.

It is unclear how long they traveled together, but they did fall in love and begin a relationship together. She was quite intelligent, and assisted The Professor in many of his endeavours, including the creation of a new species, which he called her the 'mother' of. This new race was often plagued by terrifying, psychic insectoids who saw his creations as an affront. The two were very close to exterminating the insects when one of their queens broke free of her bonds inside his TARDIS, where she had been kept for study. The insect showed signs of rapid learning and development, and it attempted to hijack the power of the TARDIS. Zoe, fearing for the race she had helped to create, cornered the creature and forced the console it was tapping in to to overload. She locked The Professor out of the room on purpose, preventing him from stopping her. She died along with the queen, causing him to stay away from the species as for several decades.

The M'haurans
The race that The Professor and Zoe had created were classified as 'felis sapiens', though colloquially named after their word for their homeworld, M'haura. Their creation was sanctioned by the High Council of Gallifrey, and overseen at every important step by the couple, going forward at various stages in their species evolution using the TARDIS to guide and influence it. Their appearance was humanoid, but with distinctly feline characteristics, a cosmic 'what if' that supposed if felines had been ascendant instead of apes.

They were a superstitious people at heart, and had several religions, all of which were taken very seriously. While there were few actual religious wars, different interpretations of the creation of the world through "The Gates of Heaven" (an analogue of the Professor's TARDIS) led to a few factions, not the least of which was the "Sisterhood". This was considered to be the Professor's favored faction, which also made them a target in the future for the insects when they later returned to M'Haura.

After Zoe's death, The Professor ended up not visiting M'Haura for quite some time, mostly due to grief, though he did become involved in other matters. During this extended absense, the planet was visited by Doctor Ross, a Dalek/Human hybrid thought to be killed by the Five. He had stolen a passing space-ship and used it to abduct humans from Earth and other places, then used their genetic material to introduce humans to M'haura, allowing humans and felines to live together in a bizzare peace. In truth his motives were far from benign; he was using both in further genetic experiments, planning to use the cunning of man with the strength and resiliance of the M'haurans as well as the technology of the Daleks to make a perfect warrior race. The Five, along with the then-Hologram Professor, arrived on M'Haura and killed Ross (again), then carefully removed the insects from the planet, which Ross had placed there again as a means of controlling the people. The Agents of Destiny entered into a tenuous truce with the Five, helping by way of removing the humans safely back to Earth. (G5: Of Gods and Freedom, Genesis and Genocide)

The M'haurans would later go on to become major players in Galactic society.

The Last Great Time War
All that is known is that the 'real' Professor did take part in it, though his exact role is unknown. He was seen by Winston in a vision, attempting to frantically repair a failing Time Lord ship while the Daleks stormed aboard.

The holographic Professor had made it an understandable goal to try and find out what precisely happened to 'him' in the war.

Life as a Hologram
After being re-awakened by the Five, The Professor has done his best to act as a teacher to them, educating them of their Time Lord heritage. He has given some of them training on how to fly the TARDIS, and has given them all some lessons on how to construct and repair a Sonic Screwdriver.

During their first mission in time The Professor's mobile emitter was destroyed by the Promethians, and was almost stuck inside the TARDIS for good until he thought to outfit a mobile emitter onto a metalroach that the Five had domesticated, which they called BUG (Biology Underfoot & Gilded). With BUG's assistance, he can now project himself anywhere he wishes, though he must upload his program into new areas if he wants to leave the TARDIS.

While he is uploaded into BUG's matrix, the two are apparently symbiotic to a degree; at Woodstock it was discovered that alcohol poured onto BUG's catalytic converter produced an effect in his processors that resulted in floating-point decimals in their programs-- which expressed itself alot like the effects of alcohol.