This lore can be found on Dromund Kaas.
Forged in a time before Sith wielded lightsabers, the ceremonial executioner’s blade was later used by Sith Lord Koval Renge who preferred the tactile weapon over his traditional lightsaber. Lord Renge used the blade to dispatch hundreds of the Emperor’s enemies and earned the title of Sith Executioner. As the Emperor’s power grew, so did Renge’s fear of his master. Fear turned to betrayal, but Renge’s plot did not escape the Emperor’s notice. As punishment, the executioner’s blade was turned on its owner. Renge resisted, but the blade struck true and broke off in his chest. Renge was not permitted the escape of death. His wounds were healed, and the tainted splinter of his blade remained buried inside him. He was then cast into the Dark Temple, the agonizing splinter a constant reminder of the Emperor’s cruel benevolence.