He was the ship's chef.
He, like his fellow crewmen had been infected with the Pox of LeChuck.
While his captain was "negotiating" with the Vaycaylians to get the summoning artifacts, Hardtack and Murkel Trenchfoot had been trusted to hide and bury the Noble Seahorse artifact that they already had.
During The Siege of Spinner Cay, Hardtack was on a ship watching the shore of Spoon Isle. Threepwood was able to slip past him in the blockade when LeChuck distracted him using a cannon on the beach. Guybrush later encountered Hardtack and Trenchfoot on Brillig Island, trying in vain to dig up their treasure.
After Guybrush sunk McGillicutty's ship, Hardtack went to Flotsam Island, where he became the court bailiff of Judge Wallace P. Grindstump, as well as a cook at his nightclub, Club 41. Stan S. Stanman convinced him that he could profit from a lawsuit with Guybrush after he was arrested for numerous crimes. He accused Guybrush of "ruin[ing] his perfectly good X," but when Guybrush confronted him about it on the stand he admitted he was lying. Judge Grindstump made him wear a girly wig as punishment for lying to the court. After Guybrush matured La Esponja Grande, he was cured of the pox like everyone else.