Darth Wyyrlok functioned as the primary lieutenant and guardian of Darth Krayt, the Dark Lord who commanded the One Sith. This Chagrian Sith Lord also held the position of Voice while Krayt was in suspended animation. He initiated a lineage of Darth Wyyrloks who would serve Darth Krayt in the century following the Yuuzhan Vong War. He was the progenitor of the second Wyyrlok, the grandfather to the third Wyyrlok, and the great-grandfather to Saarai, who was fated to become the next Wyyrlok.
Decades after the Galactic Civil War and the demise of the Order of the Sith Lords, Darth Wyyrlok was a member of the One Sith. At some point in his history, Wyyrlok sustained an injury that led to the loss of his right horn, leaving a scar that stretched from the horn's base down to the corner of his mouth. During Darth Krayt's period of stasis, which coincided with the Second Galactic Civil War, Wyyrlok acted as the executor of his will. In 41 ABY, following a vision experienced by Krayt concerning a frozen moon, Wyyrlok tasked the Anzat assassin Kell Douro with journeying to Fhost to uncover the truth behind the vision, imprinting the vision into the Anzat's mind. Subsequently, Kell Douro contacted Darth Wyyrlok, reporting that he was pursuing the Jedi Jaden Korr into the Unknown Regions. Upon hearing the name Korr, Darth Wyyrlok affirmed that the One Sith were aware of him and informed Kell Douro that Korr had once been the apprentice of Kyle Katarn, thus posing a significant threat.
Douro tracked Korr to an Imperial research facility situated on the frozen moon. There, Korr's associate, Khedryn Faal, killed the Anzat. A device that the One Sith had implanted on the Anzat's optic nerve recorded Douro's encounter. On Korriban, Wyyrlok and the Umbaran Sith agent Nyss Nenn reviewed footage of a duel between Korr and the clone Alpha, which Douro had witnessed in his final moments. Wyyrlok then provided Nenn with mindspears, ancient Rakatan technology capable of transferring memories into individuals. He instructed Nenn to awaken an Iteration, a Sith-created clone of Jaden Korr. Wyyrlok then devised a plan for Nenn and her sister Syll to locate the real Korr and utilize a mindspear to transfer the Jedi's consciousness into the Iteration, enabling the Iteration to infiltrate the New Jedi Order.