Dagan Gera

Once a paragon of the High Republic, Jedi Master Dagan Gera was undone by his obsession with the discovery of Tanalorr, abandoning the values of the Jedi Order to pursue his vision. It fell to his closest friend, Santari Khri, to snuff out those ambitions. Ever hopeful, Khri placed her former ally in a bacta tank, hoping that he would one day return to the light of the Order.

Centuries would pass before Cal Kestis would awaken Dagan.
But time had not diluted his desire. Instead, Dagan bled his lightsaber crystal and chose the dark side.

Determined to reclaim his prize, Dagan reconnects with his long-lived friend Rayvis and takes leadership of Rayvis's gang of Bedlam Raiders on the quest for Tanalorr. In a final confrontation, Dagan uses the Force to delude Cal. But the Jedi turns Dagan's power against him, revealing what Dagan fears most— the judgment of Santari Khri.

Quote from The Art of JEDI: Survivor artbook.