Even after nearly 30 years of serials, we still know very little about the Doctor's origins in a canoniacal sense. His true identity and his past remain a mystery. What we do know, is that he attended the most prestigious of the Time Lord colleges, the Prydonian academy, along with the Master, Drax and the Rani. It is also known that the Doctor was the less able of the 3 pupils, but this is due to a somewhat undisciplined, wandering mind...behavior which exasperated his former teacher, Borusa. What remains buried in the past, is what occurred in the years following his graduation from the Academy, and when he is first seen in episode 1 of "An Unearthly Child". There are two prevailing theories about his decision to leave his home on Gallifrey...

Anatomy

Like all Gallifreyans, the Doctor's physiology is quite different from that of a human. He possesses a redundant cardiovascular system (two hearts.), a respitory bypass system, and a body temperature of 60 degrees farenheight. All Gallifreyans are naturally long-lived in human terms, usually able to easily reach a lifespan of 600-700 years. However, the Doctor is a Time-Lord, gifted with the additional ability of Total Cellular Regeneration.

The exact mechanisims responsible for Time-Lord regeneration is a closely-guarded secret. One theory postulates that when the body of a Time-Lord is near death, a self-replicating swarm of nanotech machines (microscopic robots.) sets about repairing, restoring, and reorganizing the cells of their host-body. However, that theory remains unconfirmed. What is clear, is the fact that the process results in a new body for the formerly death bound Time-Lord, and oft times a radical change in personality. Some Time-Lords (Such as K'Ampo, and Romana.) can exert willful control over the regenerative process, and thereby control the nature of the new body's form, and reduce any real personality changes.

The Doctor, in contrast, has displayed time and again the symptoms of problem regeneration. For him it has always seemed to be something of a struggle, both physically and mentally. In fact on 3 separate occasions the Doctor would not have survived had the regeneration not been pushed by outside forces (The Doctor's first regeneration was assisted by the TARDIS itself, the 2nd had to be activated by the Gallifreyan K'Ampo, and the 3rd was facilitated by the Watcher, a mysterious future projection of the Doctor himself.). This may be due, in part, to the Doctor's rumored Half-Human heritage. Thus far, the Doctor has regenerated 7 times, resulting in 8 different incarnations. Every Time-Lord is able to regenerate 12 times. NOTE: It has been suggested (Mainly by the Doctor himself, during his 7th incarnation.) that the Doctor may be more than a Time-Lord, that he possesses powers and knowledge far beyond the average Time-Lord. There is some evidence to support this claim, but not enough to make the assertion a proven one.

Personality

Although the Doctor's actual personality has varied wildly from incarnation to incarnation, there are some constants. The Doctor's basic morals have remained rocksteady throught his adult life. The Doctor despises injustice, and rarely hesitates to act when faced with it. Nothing can stir him to action like the sight of opression, and it is this trait which has caused most Time Lords to consider the Doctor an embarassment. He will do everything he deems necessary to counter it, usually trying to find the least violent means possible. Most of the Doctor's incarnations hated violence as well, although a few of his incarnations could dispense non-lethal, two-fisted justice if it seemed a good thumping was needed ( Notably his third and sixth incarnations, and his fourth knew some hand-to-hand tricks as well ). Because he usually avoids violence in times of conflict, the Doctor often uses his charisma to end friction. He is capable of swaying all but the most skeptical or evil beings to his cause...which is good because the Doctor finds himself in tense situations very often.

The Doctor is insatiably curious, and displays a great love and hunger for knowledge. There doesn't seem to be any school of thought where he doesn't possess at least some basic knowledge. His knowledge of the sciences and history are particularly acute. This trait is one that seems to get him into the most trouble, as he can rarely avoid investigating a mystery or a troublesome quandry. He is capable of brilliant improvisation when he finds himself in a difficult spot. Perhaps because of his long-life, and his vast knowledge, the Doctor can be quite arrogant at times...with little patience for the failings of ordinary mortals. Conversely, the Doctor also shows great compassion...and will not hesitate to risk his own life for his friends, or for those in need.

In short, the Doctor views life as a gift, and freedom as sacred. He will fight unceasingly for the preservation of both with all the knowledge at his command.

To learn about each Doctor, starting with the First, click Here