Very powerful with the Force since early childhood, Culber grew up on Tython among the Jedi. In spite of strict training, he never let go of his feelings, passions or emotions.
His heart was always in the right place: the protection of the Republic and its denizens, standing up to evil, and destroying the threat that was the Sith Empire. But he also refused to accept that caring for people was a wrong thing or could lead to wrong, so never fully dedicated himself to the strict demands of the Jedi Code and traditions. Master Orgus’s death was the first step of Culber fall to the Dark Side: hatred, the need for revenge, pain were feelings he did not even try to suppress, but fed on instead.
Dealings with the Sith Emperor corruption, fighting former masters of the Jedi Council, led him deeper the emotional path, which resulted in Grand Master Satele refusal to grant him the title of master. That, in turn, fed his anger, and pushed him even deeper into Darkness.
Shortly after his attempt to kill the Sith Emperor, and his Jedi career stagnation began, he met Theron Shan. Theron was intrigued by this unusual Jedi, and soon the two developed a friendship which lasts until today. Theron was the person who eventually recruited Culber to the Alliance.