Nalgol, a Human from the distinguished Kuat lineage, held the rank of captain and served as the commanding officer aboard the Star Destroyer Tyrannic. This vessel belonged to the Starfleet of the Imperial Remnant. His service occurred approximately fifteen years after the pivotal Battle of Endor. Nalgol was among the four officers from the Braxant Sector Fleet whose Star Destroyers were selected to support Flim, a swindler impersonating the resurrected Grand Admiral Thrawn. This was part of a scheme orchestrated by Moff Vilim Disra and Royal Guardsman Grodin Tierce to plunge the New Republic into internal conflict, exploiting the controversy surrounding the revealed Caamas Document. To assure Nalgol and the other captains—Trazzen of the Obliterator, Argona of the Ironhand, and Dorja of the Relentless—that Flim was indeed Thrawn, Disra arranged a personal meeting between them and the supposed Grand Admiral. Despite his mistrust of Disra, Nalgol remained a dedicated and obedient officer. He accepted the directive to lead the Tyrannic, Ironhand, and Obliterator in a clandestine assault on Bothan homeworld Bothawui, shaking hands with Flim to mark the meeting's conclusion. This handshake was, in fact, a covert operation where Nalgol used his Kuat family crest ring—typically employed to deliver poison to adversaries, but now harmless—to obtain a tissue sample for comparison with Thrawn's medical records. This plan to expose the impostor and the conspiracy would have succeeded, had it not been foreseen. Under Disra's direction, Tierce meticulously altered Thrawn's records so that Flim's tissue sample would match that of the Chiss Grand Admiral.
With his doubts allayed, Nalgol, along with the other two Star Destroyers, all equipped with experimental cloaking devices, journeyed to the outer reaches of the Bothawui system. There, they concealed themselves by attaching to a comet, intending to remain hidden until they reached proximity to the capital planet for their planned offensive. However, events unfolded differently. When Imperial operatives infiltrated a New Republic warship within the capital city and initiated an attack on the planet, it appeared that the intended civil war had erupted. However, the Millennium Falcon unexpectedly discovered the three Star Destroyers concealed behind the comet, catching Nalgol off guard. Deviating from the planned schedule, he attempted to issue an attack order, but the united New Republic warships were already converging on the Star Destroyers. Recognizing the dire consequences of engaging in combat, Nalgol made the decision to order a retreat, prioritizing the safety of his crew.