Darth Revan

Revan, renowned as "The Revanchist" and dreaded as the Sith Lord Darth Revan, was an eminent Jedi Knight turned conquering Dark Lord of the Sith until, stripped of his true persona, he returned to the crumbling Jedi Order and helped defeat the Sith Empire he had established.

A human male, and acknowledged as a very gifted and powerful Force-sensitive pupil, he was trained as a Padawan by Kreia and a number of other Jedi Masters, both on Coruscant and at the Jedi Enclave on Dantooine.

He was voiced by Rino Romano in Knights of the Old Republic and by Jeff Bennet in The Old Republic.

History
Revan began as a Jedi Padawan who was said to have incredible potential from a very young age. Befriending fellow Padawn Alek Squinqargesimus, Revan very early showed a natural charisma and an ability to sway others to his way of thinking. So it was that when the Mandalorian Wars broke out and the Jedi Council did nothing, Revan vowed to fight the Mandalorians anyway, and rallied numerous Jedi to his cause.

Unfortunately, Revan's experiences during the wars rapidly began to turn him into a crueler, ruthless, and more callous individual who soon came to believe that the ends justified the means. By the end of the war, Revan's fall to the Dark Side was nearing it's completion. After ruthlessly eliminating the Mandalorian fleet above Malachor V and personally executing Mandalore the Ultimate, Revan took his remaining followers, including his friend Alek (now known as Malak) and disappeared.

Drawn to both the Star Maps left behind by the Rakatans and also the Sith Emperor, Darth Vitiate, on Drommund Kaas, Revan located the former on Dantooine, Kashyyk, Tatooine, Manaan, and Korriban, which in turn led him and Malak to the Star Forge. Unfortunately by that point they had also visited and been corrupted by Darth Vitiate, who brainwashed Revan and turned him into an agent with which he could further his agenda. Having now fallen to the Dark Side in full, Revan named himself Darth Revan and became the new Dark Lord of the Sith, with Malak as his reluctant apprentice.

Knights of the Old Republic
Using the Star Forge to create limitless fleets, Revan waged war against the Republic and the Jedi Order. At first the crusade went well, all the while Revan falling further and further into the Dark Side until eventually abandoning his previous good intentions and honor altogether and becoming completely ruthless, vicious, and power-obsessed. However this did not last long. Malak, desiring Revan's power for himself and tired of being subservient to his old friend, betrayed him, ordering his ships to fire on his bridge while he was distracted fighting a Jedi strike team sent to capture him.

Believed dead by all, Revan in fact survived, and was revived by the Jedi. Left amnesiac from the events, Revan was given a new identity with which the Jedi hoped to use Revan to finally destroy the Star Forge and stop Malak for good. Though Revan eventually recovered his memories, by that point he had returned to the Light Side and no longer wished to return to the life of a Sith Lord, instead standing against his old apprentice and also forgiving Bastila (who he had come to love) for her part in re-writing his memories.

The Old Republic: Revan
For a time Revan was able to retire and live with his wife Bastila Shan and their new son, before lingering nightmares of a world he visited during his fall to the Dark Side drove him to seek out the source.

The Old Republic
After 3 centuries of being imprisoned by Darth Vitiate, Revan descended into insanity and decided that the best way to stop the Sith for good would be to commit genocide against them, in the process succumbing to the Dark Side again. Revan was later freed by a Jedi strike team led by Barsen'thor, the group not aware of Revan's madness. There was now nothing to restrain Lord Vitiate anymore. Revan then joined the Jedi again in their struggle against Darth Vitiate and the Sith Empire.

Revan's second disappearance
However, Revan was defeated by a group of Sith and Bounty Hunters sent to stop him, at which point he disappeared in a flash of light after repeating Darth Malak's final words, stating that now he knew how he felt then. His final fate after that is unknown.

Trivia

 * He never officially speaks in Knights of the Old Republic though Rino Romano does provide some hard to hear taunts.
 * There are many continuity errors and inconsistencies regarding Revan's backstory, including when specifically he fell to the Dark Side and also how and why. Whether or not Revan is his birth name is also a point of contention, as there is some evidence to suggest it is not in fact his real name but rather an alias he took on during the Mandalorian Wars.
 * Revan was seen as a role model by later Sith Lord Darth Bane despite his being redeemed, and Bane even traveled to Lehon to seek out Revan's Sith Holocron. It was from that holocron that Darth Bane first learned about the Thought Bomb that he later used to wipe out the Brotherhood of Darkness and the Jedi they were fighting on Russan.
 * Revan and Bane were both meant to appear in the third season of Star Wars the Clone Wars as "advisors" to the Son, goading him to embrace the Dark Side more and more. The scene was cut due to conflicting with George Lucas' ideas of the Force.