Darth Valen

Darth Valen was an Force Barbarian, Dark Assault Force Trooper and self proclaimed Sith Lord. He was captured by the Empire and trained in the Dark side of the force.

Post-Capture
He completely surrendered to the Empire, and never disobeyed. For that reason, he was chosen to be taught Sith Lightning. He mastered it, and spent all of his time learning how to better control electricity.

Revolt
During the early months of the Galactic Civil war, he freed himself, captured a modified Lambda, and allied himself with a Rebellious Consortium Defiler. They returned to the prison and freed hundreds of Barbarian soldiers and Force adepts.

Behind the Story
Valens is latin for powerful. I couldn't find 'Lightning'...