Karness Muur was once a respected Knight of the Jedi Order. However, his lust for power caused him to study the nature of the dark side. He became one of the Dark Jedi during the Hundred-Year Darkness, alongside XoXaan and Ajunta Pall. He was one of the creators of creatures such as Leviathans as well. Muur fought in the Battle of Corbos and was amongst the surrendering survivors. Alongside Pall and XoXaan, Muur was exiled from the Republic and arrived on the planet Korriban with his fellow Dark Jedi. At the time he encountered Korriban’s native species he carried a yellow-bladed protosaber, which he brandished in their presence as a display of his superior power.

Muur and his fellow Dark Jedi recognized the potent and untapped Force–sensitivity of the Sith race, and immediately sought to enslave them through the dark side of the Force. After conquering the Sith species, Muur like his fellows anointed themselves as Lords of the Sith, and were the very first to don the honorific title.

Karness Muur also possessed his own personal Sith amulet, one imbued with tremendous dark side power, should the wielder have the strength to dominate it. Crafted by his fellow exile, Sorzus Syn, the Muur’s talisman afforded Muur the power to transform those in his close proximity into mindless thralls for him to command. When the Talisman was found not to work on Force-sensitives or certain alien species, Muur further engineered the Rakghoul plague, an infection which could be spread by those already under his thrall.

With his army of rakghouls, Muur intended to use them to rule the galaxy. He also created the Codex of Karness Muur around this time, in which he illustrated the power of his beloved Talisman and its intentions for the Sith. At this point he was already using a modern lightsaber, as opposed to a protosaber. Muur was not without rivals among his brethren, though. One such enemy was another Sith Lord named Remulus Dreypa who created an specialized stasis pod to capture and neutralize Muur and the power of his Talisman. However, Dreypa was never able to contain or capture Muur within his oubliette.