After Tenebrae killed his father in 5103 BBY, he imprisoned his spirit in the holocron, so he could continue to torment him. Years later he performed the Ritual of Nathema, wiping out all life on the planet and achieving immortality. Tenebrae, now called Vitiate, kept the holocron in his personal vault under the Sanitarium, the only structure that remained standing on Nathema over time.
Lord Dramath imprisoned inside the holocron.
Imprisoned and tormented for over a millennia, Dramath eventually learned that the holocron could serve as a prison for not just him, but Vitiate as well, and even destroy him under the right circumstances. In 3630 BBY his holocron was found in the Sanitarium by Lana Beniko and the Alliance Commander, who by then housed the spirit of Vitiate in his head. Heeding Dramath's counsel, they released his spirit and took the holocron with them in the hope of destroying the Immortal Emperor once and for all.
Wearing Valkorion's visage, the Commander finds the holocron inside their mind.
The Commander of the Alliance soon claimed the Eternal Throne, after which Vitiate announced his long-gestated intention of fully possessing his body. He pushed the Commander's identity deep into the depth of his mind, where representation of the holocron was also present. In the depths of his mind, the Commander found the holocron, using it to first restore their physical appearance and then to free the spirit of Vitiate's daughter Vaylin from his control. Vaylin's brother Arcann used the physical holocron to join the Commander in his fight and the three engaged Vitiate, the Commander able to use the holocron to drain his power. Eventually Vitiate destroyed the representation of the holocron inside the Commander's mind, but the physical holocron remained and was used by Senya Tirall to join their children and the Commander in finally destroying Vitiate's existence.
Dramath's holocron appears in Star Wars: The Old Republic: Knights of the Eternal Throne during "Chapter VII: Into the Void" and "Chapter IX: The Eternal Throne". The player can release Dramath as a Light Side choice or keep him imprisoned as a Dark Side choice. In this case, Dramath's spirit will join the player in the fight against the Immortal Emperor, but will be eventually obliterated.