Darth Raithus was the powerful leader of the Third Order. His reign began when order 66 took place in the jedi temple on Coruscant. He and his friend Mara were two of the younglings that survived this jedi extermination. This led the young Jedi apprentice to the dark side. Eventually rising to power as Supreme leader of the Third Order, he fought Mara Kenobi, revealed to be Obi-wan's niece with no explanation of how that could be.
by the way, Raithus wears a mask made out of pure dark side energy.
