This duel was between the Barsen'thor and Terrak Morrhage, who was using Parkanas Tark's body at that time.
When Master Yuon Par fell ill, it was up to her apprentice to find a cure. Finding the three Noetikons, the Barsen'thor learned that the plague was created by Terrak Morrhage, and the Barsen'thor also learned of how to counter it-with the use of a powerful Shielding Technique. Upon learning this technique, the Barsen'thor healed Yuon Par, and traveled around the galaxy, finding afflicted Jedi and healing them. Finally tracking the plague's source to Lord Vivicar's lone flagship in the distant Outer Rim, the Barsen'thor set out to face Vivicar.
Barsen'thor was met by a towering man—Vivicar. There, it was known for certain that Vivicar had indeed been corrupted by the spirit of Terrak Morrhage. The Barsen'thor engaged the boastful Sith Lord in a fierce duel.
Despite Vivicar's dark tricks, he was no match for the Barsen'thor, who overpowered him. The Barsen'thor used the Shielding Technique to expel the spirit of Terrak Morrhage from the innocent Parkanas Tark's body, redeeming him as the Jedi he formerly was.
The Barsen'thor returned to the Jedi High Council, which named the Jedi as the third Barsen'thor in history.
- Star Wars: The Old Republic Encyclopedia