Not much is known about Trigit's early career, only that he served under Isard. Upon her apparent death over Thyferra in 7 ABY, he left the Imperial Starfleet and went rogue, eventually hiring out his Star Destroyer to Warlord Zsinj. He leaked false information to the New Republic that led to an the destruction of an entire squadron of X-wings (Talon Squad, of which there was only one survivor). Emboldened by this, he then attacked Folor, but the newly formed Wraith Squadron managed to escape destruction. Trigit himself would then proceed to escape a trap set for him, at the cost of two other vessels.
The next trap set by the Wraiths he would not escape from. With the Implacable's unshielded and immobilized, Trigit ordered the self-destruct sequence, sacrificing 35,000 people rather than surrender. His attempt to flee in a modified TIE/IN Starfighter were foiled when Myn Donos, the survivor of Talon Squadron, fired two proton torpedoes at his ship, annihilating him.
In addition to being a free ISD (which is never a bad thing) Trigit serves as a fleet commander, providing an extra 10% Damage and 10% Health to friendly ships. This may not seem like much, but he as there are three field commanders in Era 1 other than Isard, he be paired with a fleet containing an Executor-class Star Dreadnought. With a ship that provides that much firepower, suddenly 10% more damage becomes huge. It will also keep your ship alive that much longer. Alternatively, he, Krennel and Harrsk (or Isard) could be combined to give 15% Damage, 10% Health, and 5% Shields (now a much more formidable bonus).
In Hunt For Zsinj and Into The Cluster, Trigit is much less useful because Zsinj is a much better fleet commander. He still can be used as the leader of a secondary task force, however.