The Death Lords were an ancient order of ruthless warriors from Ketha, sworn to protect it, the Eighth Doctor reflecting that they'd died out aeons ago. Their technology included bladeships and they were "basically immortal."
During their last stand when the Citadel was lost, the Elders having betrayed them, the Death Lords turned against their leader Vakrass and he was left for dead, drifting through the blackness of space until he eventually became the "last of the Death Lords." (AUDIO: The End of the Beginning)