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.

Being very charismatic and possessing notable leadership qualities, by 3,964 BBY he was a Jedi Knight respected enough to amass a notable following that argued for Jedi intervention in the Mandalorian Wars. Though opposed in this by the Jedi Council itself, Revan could not be dissuaded. Revealing the horror of the Mandalorians' genocide of the Cathar, Revan bolstered his support base and then quickly circumvented the Council, exploiting a technicality that forced it to begrudgingly "sanction" the intervention he desired. With the Council sidelined, the charismatic young Jedi and his closest friend, Malak, were able to recruit and lead a faction of the Jedi Order to war without fear of reprisal.

Recognized as a talented military tactician and strategist, and the Jedi Order's most powerful champion, Revan directed the Galactic Republic to victory after assuming command of its forces in 3,961 BBY, finally ending the conflict the following year with the defeat and execution of Mandalore the Ultimate, the destruction of Malachor V and the disarmament of the Mandalorian Neo-Crusaders—acts which earned him a reputation among the Mandalorians as Revan the Butcher. In the wake of this triumph, Revan, his loyal Jedi followers, and the third of the Republic fleet that remained under his direct control ventured into the Unknown Regions—ostensibly in pursuance of Mandalorian stragglers—and ceased all communications with the known galaxy.

In those unknown regions of space, on Dromund Kaas, Revan and Malak came face to face with the long hidden Sith Empire and its Emperor. Thus, having already embraced the seductive Sith teachings he encountered at the Trayus Academy on Malachor V, Revan's induction into their traditions was finally completed. Bid by his newfound master to acquire the Star Forge—a superweapon of the Infinite Empire—on his behalf, Revan successfully tracked down the last Rakatan Star Maps required to reveal its location. Upon securing the ancient space station, however, he returned to the civilization he had left behind openly as Darth Revan, proclaiming himself to be the Dark Lord of the Sith. Commanding the continued obedience of many veterans of the Mandalorian Wars, and alongside the man who was now his Sith apprentice, Darth Malak, Revan betrayed the Jedi, turned against the Republic, and plunged the known galaxy into the Jedi Civil War.

Utilizing the Star Forge to spawn an immense armada, Revan cut a carefully calculated path of conquest through the Outer Rim, building his own powerful Sith Empire to which new converts regularly flocked. Though the Republic staved off total defeat for two years, thanks to the extraordinary battle meditation of the gifted Jedi Bastila Shan, Revan's ultimate triumph seemed inevitable until he and Malak were ensnared by a Jedi trap. As a Republic fleet engaged that of the two ruling Sith, a strike team led by Shan boarded Revan's flagship and battled its way to the Dark Lord. Moments before the Jedi engaged Revan in combat, however, Malak—sensing an opportunity to be rid of both the Jedi and the Master whose power he coveted—had his own vessel open fire on the distracted Sith Lord's bridge. Caught by surprise, Revan was incapacitated by Malak's attack and then captured by the strike team while his traitorous apprentice, believing his Master destroyed, seized control of his Empire.

His mind shattered, his memories scattered, and soon thought dead by the galaxy-at-large, Revan's life was preserved by none other than Shan, an act that forged a Force bond between them. Either unable or unwilling to restore their prisoner's true self, but requiring the knowledge buried within his mind, the Jedi Council used the Force to rebuild Revan with a new identity loyal to the Republic. Almost one year later, after Revan, still oblivious to his true past, rescued the captive Shan alongside Commander Carth Onasi and an eclectic band of allies on Taris, the Jedi Council on Dantooine opted to retrain him. Reawakening to his former skills and charged with unearthing the source of Malak's colossal fleet, Revan and his loyal comrades thwarted all obstacles and adversaries as he and Shan were guided by shared "visions"—in truth Revan's own memories—to the Star Maps on Tatooine, Kashyyyk, Manaan, and Korriban.

In the midst of this odyssey, the group was ensnared by Admiral Saul Karath, commander of the Sith fleet, and imprisoned aboard the Leviathan. Though Revan and his allies escaped, killing Karath along the way, Darth Malak confronted his former Master, revealed his true identity and ultimately recaptured Shan, the woman Revan had come to love. Continuing in the face of this loss, Revan and his allies successfully discovered the final Star Map and the location of the Star Forge. There, in the Rakata System, Revan rejected the darkness of his past, turned Shan—whom Malak had broken to his will—back to the light and vanquished the reigning Dark Lord, playing his part in the battle that brought the war he had instigated to a close.

Two years later, after having driven the warring Sith factions from Korriban, Revan—with more memories returning—left the known galaxy behind on a solitary quest against the true Sith Empire. As of 3,641 BBY, he was thought to have never returned.

Years later, Meetra Surik traveled into the Unknown Regions to aid Revan in his fight against the true Sith. She then discovered that he had been captured by a member of the Dark Council, Revan was freed by Meetra Surik and Scourge, one of his captors. The trio attempted to kill the Emperor, but Scourge turned on his allies when he realized their mission was doomed and killed Surik.

The Emperor held Revan prisoner for the next 300 years, feeding off of the Jedi Knight while he kept him in stasis in The Maelstrom. Revan spent his imprisonment fighting the Emperor, influencing the Sith to seek peace in the Treaty of Coruscant. Not long after the treaty, Meetra Surik's Force ghost appeared to a Jedi and told him of Revan's location, causing a strike team to infiltrate the prison and free him.

After traveling to Tython and informing the Jedi Council of everything he knew about the Emperor, Revan traveled to the Foundry and began to build an army of battle droids. In response, the Emperor sent a strike team of his own to destroy Revan, which infiltrated the station and defeated the Jedi Knight.

In later years, Revan was revered and remembered as a very powerful Force user in galactic history. Many learnt off of his teachings and his actions;Darth Bane basing his philosophies and rules over many things done by Revan. Revan had many Cults devoted to him and thousands of years later, a Sith Lord came up with his new name by basing it off Revan; naming himself 'Darth Rivan'.

(From Wookiepedia: The Star Wars Wiki)