Revan was created to be the protagonist of the RPG game Star Wars: Knights of the Old Republic made by Bioware. Initially, not much information was provided for him (Knights of the Old Republic allowed the player to make decisions regarding the character for their individual game stories) but over time his story was expanded and more information was given.
Major Story Arcs
The exact details of Revan's early life are a complete mystery in Star Wars world aside from a few comments from Kreia. There were some that claimed he had been born beyond the Outer Rim, his parentage and homeworld remain unknown. Regardless, he was eventually deemed suitable for instruction in the ways of the Force by the Jedi Order, but no information of how old he was when he was scouted is available. During the game when questioned by Bastila one of the answers to where were you born question, is Beyond the Other Rim which reinforces the claim.
Life at the Jedi Order
According to Kreia's claims, it was she who was in charge of Revan's initial instructions in the Jedi Arts and, along with his closest friend Alek, Revan was trained both on Coruscant and at the Jedi Academy on Dantooine. During the time both Revan and Alek visited Jedi Master Zhar Lestin for additional training, the elder Jedi noted Revan's "insatiable" desire for knowledge in particular. At the time, he dismissed it as mere eagerness, believing the youth to be a future champion of the Jedi Order. Master Vrook Lamar, on the other hand, later stated that Revan was perhaps too eager to learn more about the Force, and had sought knowledge of ancient "Sith magics."
Revan was said to have left Kreia's tutelage entirely, going on to study beneath numerous Jedi Masters, including the aforementioned Lestin, as well as Master Dorak, the Jedi chronicler of the Dantooine Jedi Enclave, and Arren Kae. Some years later, the former Jedi Mical known in KOTOR II (Knights of the Old Republic 2) as apprentice claimed that Revan had deeply studied the process of Force Bonding, among other techniques, during this period. Eventually, however, it was said that Revan returned to his first Master Kreia when "he realized there was nothing more to be learned from the Jedi except how one could leave them forever."
By 3,956, the general thoughts of the Jedi Masters on Dantooine was that, though one of the most promising Padawan in the history of the order, Revan had been headstrong, proud and far too quick to dismiss the dangerous lure of the dark side or of a possible dangerous situation. Before 3,963 , Revan, alongside Alek, attained the rank of Jedi Knight.
Revan was born beyond the Outer Rim; it is not certain where. Revan's real name is also unknown. Revan was taught the ways of the Force by many masters, some of which included Zhar Lestin, Dorak, Arren Kae, and Kreia before he left for the war. Revan went back to his first master to ask him what was the best way to leave the Jedi Order. Revan studied the force on the system of Dantooine. After the Mandalorians started their crusade, the Jedi had decided not to act while the entire Republic was being destroyed.
The Republic then asked the Jedi for their support, but all they did was meditate on the situation. Then a small group of Jedi actually went against the Jedi Council in order to join the resistance, and were later called Revanchists. The head of this was Revan - who adopted the name given to him by news media, the Revanchist - along with his now new apprentice, Alek This led to a change in the war, leading to the Republic victory over the Mandalorians at the Battle of Malachor V.
It is after the war that Revan then left into the Unknown Regions only to come back as the new Lord of the Sith. Some time after, Revan began a war on the Jedi and the Republic, his Sith consisting of former Revanchists. It is later in the war that the Jedi sent a small squadron of Jedi to attempt to capture Revan but failed when Malak himself opened fire on his master's ship. This left Revan on the verge of death, from which Bastila managed to save him from by sustaining him with the Force. Revan was alive but his mind was destroyed.
The Jedi Council took the opportunity to plant a new personality into the Sith Lords mind, one loyal to the Republic and the Jedi Council. After going on a quest to find the maps to the Star Forge and follow the path of Malak and Revan from the past, Revan falls into a conflict with Darth Malak. After a lengthy discussion Malak reveals to Revan that he is infact Revan. Only to end up running from the battle Revan walks away wondering about himself. While hunting down Malak, Revan ask his fellow crewmates questions about himself ranging from how they feel about knowing he was once a dark lord to what he was like in the past. After finding the Star Forge and fighting his way to Malak the two again battle.
After defeating Malak and The Star Forge (a giant space station/factory built by an ancient alien race called the Rakata) it is said that Revan then left once more into the Unknown Regions to fight what Kreia called "The True Sith." He was never heard of again.
The Old Republic: Revan
In the Old Republic novel series based nearly 4000 years before Star Wars: A New Hope shares Revan's adventure and explains his disappearance and re-appearance cameo in the Star Wars: Old Republic MMO.
Revan has defeated Darth Malak after being "re-programmed" by the Republic and the Jedi Order and has since been called the Saviour of the Galaxy. Despite his victory and recognition by the Jedi order, Revan still fails to find peace due to his loss of memories and disturbed nightmares of his mysterious past. Since his moment of triumph, Revan has spent his time with his wife Bastilla, trying to finally settle down on Coruscant but constantly has nightmares that he has no memory of and due to his lack of sleep, set's out to find out the truth to his "visions".
Revan meets up with his former ally and close friend Canderous Ordo, a Mandalorian warrior that helped Revan to defeat Darth Malak and soon after left his people due to their disparity and was considered a traitor. Revan and Canderous traveled to the planet Rekkiad, a planet believed by Revan to be the place where he hid Mandalore's mask after the Mandalorian Wars. Revan believed if he retraced his steps of the past, it would help him regain his former memories.
Landing on Rekkiad, Canderous and Revan regrouped with Clan Ordo in order to help them retrieve Mandalore's mask. Canderous reunited with his wife and clan leader Veela. Needing their help to traverse the frozen wastelands of the planet, Revan decided with Canderous that it was in their best interests to help out Clan Ordo rather than stand against them. Revan kept his identity as a Jedi secret from the Mandalorians because of their deep hatred of Jedi's due to the war between them. After being ambushed by the opposing clans, Revan had no choice but reveal his identity as a Jedi to turn the tides of the battle but to his relief, only Veela and a few other pilots saw the truth.
Once finding the cavern where Revan hid Mandalore's mask, Revan briefly had visions of a planet in the Unknown regions of the Galaxy while Veela and a few other members attempted to ambush Revan and Canderous. After quickly dispatching them, Revan encouraged Canderous to become the new Mandalore in order to unite his people and he became Mandalore the Preserver.
Revan then set off alongside his trusty droid T3 to the unknown regions and more specifically, the forgotten planet of Nathema. The planet itself, which was once home to the Emperor of the long forgotten Sith Empire, was completely void of the force, as if it was just ripped away from existence. At the same time he reached the planet, he was shot down from retreating Sith Lord's Darth Nyriss and Lord Scourge. They captured Revan and brought him to the heart of the Sith Empire and the Sith's home planet: Dromund Kaas.
Revan was imprisoned for the following three years and interrogated by Scourge for information about why he was at Nathema although learning almost nothing due to Revan's loss of his memories. Meetra, Revan's former apprentice and most trusted Lieutenant during the Mandalorian Wars, decided to speak to Bastila about Revan's disappearance. They both decided that she needed to set out and find Revan. Bastila told Meetra that if she were to find Revan that she wanted to give him a holo-vid of the birth of his son and his old helmet that he wore, hoping that it would flush back his past.
Revan, on the other hand to be kept at a weakened state, was given drugs so he wasn't able to reach out to the force. He decided rather than fight against Lord Scourge, he planned to toy with the Sith Lord, telling him false visions of his eventual escape in hope that the gullible and arrogant Sith would be the key to his escape. Meetra and Scourge eventually teamed up after learning of the Emperor's true nature and plan to attempt to overthrow the Republic, which could result in the end of the Sith for good.
After Scourge convinced the Emperor that Nyriss was a traitor as was the rest of the Dark Council, Scourge returned to Meetra to plan their break out of Revan. As they entered into Nyriss' palace with Meetra disguised as Scourge's slave, they made their way to the dungeon when the Emperor's forces assaulted the Dark Lord's fortress. Finally reaching Revan's cell, Meetra gives her old master his worn helmet and in a swift rush, his brain overloads from all the images that flushed through his brain at once. As his body laid sprawled on the floor, Darth Nyriss learned of Scourge's betrayal and engages Scourge and Meetra in battle, easily over-powering them. As she was about to land the killing blow, Revan steps out of his cell, wearing his old helmet and almost too easily dispatches Nyriss by re-directing her own attack as he simply states, "I am Revan reborn".
Revan, Meetra, and Scourge retreated from the destroyed Palace to a cave on the outskirts of the city, planning their attack on the Emperor. Still wearing his helmet, Meetra believed him to be lost to his memories but as soon as Revan spent the entire night watching the holo-vid that Bastila left him of her and their son, he took of his helmet and Meetra felt relieved. The next morning, they made their way to the Emperor's palace and had successfully infiltrated. Scourge and Meetra fought off the Imperial Guard as Revan made his way into the throne room.
Previously, the Emperor had caught Revan off guard, wiping his mind and making him slave and weapon against the Republic. This time, Revan was more powerful and ready for what the Emperor was prepared to do. They briefly exchanged attacks before Revan became over-powered by the unbelievably powerful Dark Emperor's force lightning which melted Revan's skin and forced him to his knee's. Scourge and Meetra quickly came to Revan's aid, but Scourge being the coward he was and afraid of death, betrayed Revan and murdered Meetra. While Revan dropped his guard, the Emperor unleashed his power on him and easily dispatched him. As Scourge was about to finish him, the Emperor stopped him abruptly and told him that he has plans for Revan.
Revan spent the next three thousand years imprisoned by the Emperor while he fed of his power and scoured his mind for information about the Republic. But for the sake of his son and his family, Revan resisted the Emperor, even infiltrated the Dark Lord's mind himself, potentially saving the Galaxy again and stopping an invasion of the Republic.