Tirossk, a Bothan male, held the rank of Captain and served as the commanding officer of the Lancer, which was a Corellian frigate assigned to the New Republic's Rapid Response Task Force.
During the Battle of Mindor which took place in 5 ABY, Tirossk took part in the conflict. Following the destruction of General Luke Skywalker's flagship, the Justice, by a gravity bomb deployed by Lord Shadowspawn, Tirossk, due to his higher ranking, assumed the role of acting commander for the Rapid Response Task Force.