In 2365, Nahsk, along with his brother Krit and associates Hain, Larell and Morn, planned and executed the Lissepian Mother's Day Heist, a notorious robbery that occurred on the planet Lissepia, in which one thousand bricks of gold-pressed latinum was stolen from the planet's Central Bank.
Though all thieves managed to escape the authorities on Lissepia, Morn double-crossed Nahsk and the others by melting down the latinum and storing it in his second-stomach, with the aim of keeping it for himself following expiration of the statute of limitations.
In 2374, Nahsk and his brother attempted to find the latinum stolen in the heist. They double-crossed the others who participated in the crime, with the intention of keeping the haul for themselves. However, they and the others were unsuccessful and later arrested on the space station Deep Space 9. (DS9: "Who Mourns for Morn?")
Nahsk and Krit are the only two of their species seen on-screen. Their species is not named in the episode.
The script for "Who Mourns for Morn?" states the pronunciation of Nahsk's name as "NAUSK". It goes on to describe both him and his brother as "well-dressed, but there's something sinister about them that says organized crime." Of Nahsk himself, it says, "Nahsk is the "muscle" of this duo, and a bit slower than his brother."