Darth Revan

Dark Lord of the Sith during the Old Republic. He started out as a Jedi who came off victorious in the Mandalorian Wars at Malachor V. The planet, filled with death and Dark Side power was more than enough to make him give into his anger. He started to study at the Trayas Academy where he adopted the title of Darth Revan, he and his apprentice Malak then started the next battle, the infamous Jedi Civil War.

To ultimately pwnt and dominate everything. This is in reference the awesome Sith Lord.

In the Star Wars universe, a sith lord of unknown gender who lived approximately 4,000 years Before Battle of Yavin. Led the Republic to victory in the Mandalorian Wars before disappearing in to the Unkown Regions with much of the Republic Army. The prodigal knight reappeared as Darth Revan, lord of the sith, and launched a successful campaign against the Republic before being betrayed by Darth Malak. A ship-to-ship attack destroyed Revan's mind and left the dark lord in a coma. The prodigal knight's mind was reprogrammed by the Jedi Council, and the reformed sith lord was sent to find the source of the vast resources Darth Revan had employed against the Republic. After the completion of this mission and the death of Darth Malak at Revan's hands, the saviour of the Republic again disappeared into the Unknown Regions. Historians have yet to discover the prodigal knight's fate.

A character from Star Wars : Knights of the Old Republic.
Revan is dude a who went to the highest extremes to ensure stability and peace in the Galaxy.
He became a Sith Lord out of necessity after experiencing a vision of the future, which showed a large Sith Empire hailing from the Unknown Regions taking over the known Galaxy.

He believed the Jedi and the Republic were woefully unprepared for the coming Sith threat, so he planned to conquer the Republic and transform it into a militarised Sith Empire in order to fight against this coming threat.

He almost conquered the Republic by:
Converting Jedi to his cause
Assassinating corrrupt senators and replacing them with ones loyal to his cause
Keeping Shipyards intact to fuel his Sith armadda

Revan's own obsession with stopping this vision from coming true was what led to his downfall. He was betrayed by his own apprentice, Darth Malak. Revan's constant obsession with his long term plan made him blind to the anger and rage consuming Malak. When he finally realised his apprentice's intent to kill him and take the mantle of Dark Lord, it was too late.

Revan surived Malak's betrayal, but his mind was shattered and his memories were lost.