The story of Darth Revan is a long one. It begins during the mandalorian wars, Revan, then a jedi knight, and his best friend, Alec, were restless and urged the council to aid the Republic. However, the jedi order did not share Revan's enthusiasm, Revan and Alec found an ancient ruin on Dantooine, housing a Star Map. He visited Seven planets in search of these, leaning more to the dark side as he went. When he finnaly discovered the Star Forge, he gathered many jedi and attatcked the Mandalorians. After the wars, Revan and his army disapeared. When they returned Revan declared himself Darth Revan, and Alec, Darth Malak. They broke the republic.
Finnaly, Malak turned on his master and attacked his ship. While he did this a jedi strike team confronted Reven, headed by skilled jedi knight Bastilla Shan, The attack by Malak rendered Revan uncounsious and killed all of the jedi, save Bastilla.
Bastilla saved Revan and took him to Dantooine, where the jedi wiped his mind. Revan aided the Republic as a Republic Soldier on the Endar Spire, where Bastilla recently took comand.
The ship was attacked Revan was aided by Trask Ulgo to the Escape Pods, where he and Carth Onasi escaped to Taris.
Revan regained his jedi abilities and went on the same path to the Star Forge, This time on the Path of Light.
Along the way Bastilla turned to the Dark side, but when Revan made his way to the command deck of the Star Forge he turned her back t the Light side and persuaded her to use her unique Battle Meditation to aid the ongoing Republic attack.
Revan then sought down Malak, trying to persuade him back to the light, it could not be done. Revan Killed Malak, then escaped the imploding Star Forge. One year later he left for Sith Space, looking for what caused the Mandalorian wars. He was never seen again.