Before TOR, Bioware had already developed a game set in the Star Wars universe: KOTOR, best role-playing game of the year 2003. Moreover, KOTOR, of which several members of the development team are part of the developer executives of TOR, is the main source of inspiration from the Extended Universe used for our mmo.
As a role-playing game, KOTOR is full of choices which more or less influence the continuation of the adventure. Sometimes contradictory choices. Each player can therefore develop their main character as they wish. The stories of the Extended Universe unfolding in the entourage have tried to preserve the mystery to cover the maximum of possibilities chosen by the various players. But after a while, for the purposes of one role play or another (TOR included), elements began to be formalized. There are now enough of them to draw a fairly reliable official version. I won't give it to you literally, many Star Wars encyclopedias already doing this well enough. Here are especially the elements if you want to redo a game by sticking as much as possible to the barrel.
Attention, the following requires a color code. The parts in blue are confirmed, official. Whether through the services of Lucasarts, role-playing games referring to the period, the various Star Wars novels by Drew Karpyshyn and even TOR. In red, it is more like theories. I reassure you, I do not take them out of my playing experience. They are bundles of presumptions deduced from the same sources cited above, not clearly announced in them but including logical associations.
Before talking about the story, it is worth introducing the main character. You've certainly already finished the game, so I won't spoil you by telling you that this is Darth Revan, Jedi knight turned Sith lord and amnesiac as a result of the actions of the Jedi Council. I will not dwell on his past, of which we still only know the broad outlines. But TOR's main revelation is his face, formalized for the first time.
We had already learned for paper role-playing purposes that Revan was a man. If we look at the list of potential faces (image below) of KOTOR, the closest is the second to last in the right column. I reassure those who don't like this face, haircuts evolving over the years, all non-black faces and with brown eyes are potentially acceptable. Note all the same in the Chronology of TOR showing him before the start of KOTOR, he has even longer hair. Counterbalanced by the time spent in the novel Revan, in conditions which more than justify that his hair grows back during this period.
For the class, there is nothing official. The Revan novel shows him using two blasters at the same time. This seems to push the soldier (who starts the game with a rifle) away. And for the Jedi class recovered from Dantooïne, the cover of that same novel shows him with a green consular lightsaber. Inside and in TOR, he uses the lightning bolts of the inquisitor, mirror of the consular. Finally, his appearance in KOTOR II with two lightsabers is not considered canon, but has inspired many designers. The niman, that fighting style, is also known as the consular style (yes, I know. Bioware got stuck at that level in the design of classes).
For the KOTOR scenario, it is considered that all quests are completed. That is to say, Revan is the go-getter champion on Taris, Manaan and Tatooïne. He won the Gladiatorial Tournament on Taris. But he also played the henchmen for the underworld of Taris and eliminated the Genoharadan leaders of his day. As for how all of these quests end, it's trickier. Most are secondary, and do not affect the game and galactic destiny. The end of the game is bright, but it's not about how to play here, it's just a (obvious) choice in one of the last main quests. In the novel Revan, the hero is wary of the Jedi Council, and has spread this suspicion to those around him. If you want to make your character more obscure, this can therefore be justified.
For the main quests, some planets are as unconstrained as the side quests. Starting with Taris, the very first. The bombing of Darth Malak destroyed all records and left only a handful of survivors telling conflicting stories. Impossible to draw a truth from it. The only quest resumed afterwards (in TOR) is a secondary quest, that of the refugees from the most underground of the levels. They left for the promised land before the bombardment, but it did not spare their destination ...
With Dantooïne revolving almost exclusively around the Jedi formation, this one works just as well either way. The only quest with consequences is the confrontation with Juhani. She must survive, and you must convince her to return to the Jedi to join your party. For the rest, another Malak raid will destroy the official archives a little later. In KOTOR II, not everything has been looted in the enclave yet, and the Temple of Coruscant has been emptied by its archivist himself.
The following planets can be visited in any order. I will start with Tatooïne, which is in line with the previous two. The only mandatory quest in relation to the cannon is the recruitment of HK-47. Many sources speak of the deal made with the Sandmen, but none is official. And since it is only one tribe anyway, this agreement would have no real consequences.
On Kashyyyk, here we get our last companion, Jolee Bindo. The period sees the wookies rebelling against the Czerka and driving them from their home planet, also closing their spaceports to all potential visitors. This is a trick to take into account the two possible endings of the planet scenario. Nothing tells us if we are responsible for this rebellion or if it occurs in the months / years that follow. But if you choose to support Zaalbar's father rather than his brother, you still find yourself really involved.
On Manaan, it's the other way around. The ending presented is rather related to obscure choices. Kolto production will drop dramatically, destroying this source of medical panacea. But TOR qualifies the official statement. We still use a lot of kolto there anyway, it's not the tech healers who are going to contradict me. So, a cataclysm that has not yet taken place? Or reserves that are still very important to last?
The last planet in the bundle is Korriban. Here, it is KOTOR II who teaches us that in the following year, an impressive number of Sith killed each other here trying to seize power. We can start this conflict by killing the two leaders of the Academy or by tightening the bonds with Yuthura Ban as much as possible and sending him to join the Jedi.
Visiting all of these planets allows us to unlock the Unknown World, aka Rakata Prime, aka Lehon (renamed by Drew Karpyshyn in the first Darth Bane novel). There is no official version on which faction we are allying with. Either way, this is a race heralded on the verge of extinction and on the verge of extinction (for objections, TOR's rakatas are not the same). A rumor announced a few months ago Lehon in the list of planets in the works to join the universe of our mmo. If this holds true, we may have more information on the subject.
On the other hand, once entered the temple, things become very codified. This is the moment of choice that I told you about earlier. During the confrontation with Bastila, she offers to join her and ally against Malak. We must refuse, and stay on the side of the Jedi. Bastila flees to the Star Forge, and becomes the penultimate boss of the game. New confrontation after defeating her. The discussion choices to make are the great declaration of love to bring her back to the bright side (otherwise, no future Satele Shan). So we can go face Darth Malak in the official end, that of the bright side and redemption ...
I reassure all those who do not like this version of the game. With the Mass Effect and Dragon Age II series, Bioware has introduced a novelty in role-playing games: an official version (predetermined main character) but also the possibility of everything send fly so as not to follow what the developers want. You are therefore always free to reinterpret in your own way. But don't be surprised if any new reference from the Star Wars universe comes to talk about this period by following what I've marked in blue.