On the planet Korriban, at the Sith Academy, Tremel served as a male Human Sith Overseer. His responsibility during the Cold War was to identify and select suitable acolytes for Sith training. He oversaw the arrival and subsequent training of a promising acolyte, who later became his apprentice.
For a period spanning decades between the Great Galactic War and the Cold War, Tremel managed and judged the trials for acolytes seeking entry into the ranks of the Sith. He intentionally designed these trials to be exceptionally challenging, with the goal of ensuring that only the strongest candidates survived while eliminating the weaker ones.
Tremel directly participated in the selection and instruction of a promising new acolyte, intending for this individual to become a rival to Vemrin. Vemrin himself was an acolyte vying to become the new apprentice of the influential Sith Lord Darth Baras. Tremel viewed Vemrin as an "impure" Sith due to his origins on Balmorra, rather than the traditional Sith Worlds, and the absence of any Sith lineage or Force sensitivity in his family history. To give Vemrin's rival an advantage, Tremel expedited the acolyte's arrival on Korriban.
Tremel's inflexibility ultimately led to his downfall, as Baras ordered his new apprentice to eliminate him. In the ensuing confrontation, Tremel was defeated and killed by his former student, who then presented Tremel's hand to Baras as proof of his death. Tremel's daughter, Eskella Gryton, also met her demise at the hands of Baras's apprentice when she sought vengeance for her father's death. His protégé would eventually earn Baras's favor, engaging in a duel with Vemrin inside the Tomb of Naga Sadow and killing him.
Tremel possessed a composed and disciplined demeanor, demonstrating unwavering loyalty to the Empire. He expressed dissatisfaction with the admission policies of the academy and, more broadly, with the direction the Empire was taking during its conflict with the Galactic Republic. His resistance to embracing these changes was a significant factor in Baras's decision to have him assassinated.
Tremel was skilled in combat with his single-bladed Sith lightsaber. He also wielded some power stemming from the dark side of the Force.
Paul Darrow provided the voice for Tremel in Star Wars: The Old Republic. Darrow's death occurred on June 3, 2019.
The Warrior has the option to either kill Tremel or allow him to live. If Tremel is killed, Eskella will attempt to avenge him, but she will be killed in the process. If the Warrior spares Tremel's life, an enraged Eskella will eventually find him in hiding, attack him, and Tremel will be forced to kill his own daughter. Only then will he desire revenge on Baras for what he had done to him.
Later, at the request of Darth Vowrawn, he will emerge from hiding to witness his former student defeat Darth Baras and put an end to his claim as the Voice of the Emperor.