Yrssk was a male Trandoshan who worked for the Galactic Republic as an intelligence agent. During the Republic's latter years, while Yrssk was middle-aged, he and his fellow agent Klieri were sent to the planet Nyriaan to investigate the Deluge Experiment, a secret project that had been initiated by the Corporate Sector Authority to alter the world's climate. On Nyriaan, Yrssk betrayed the Republic and began working for the CSA, while maintaining the pretense that he was a loyal agent, and he also cultivated a number of allies among the world's native groups, including the Nyriaanan Malvina clan and some mutant Sith known as the Children of the Tempest. The CSA eventually assassinated Klieri and Yrssk broke off contact with the Republic, and a group of Republic operatives were sent to the world to look for the two agents. Yrssk attempted to manipulate the Malvina clan into killing the agents, by claiming that the operatives were miners who had been sent to establish a mine on Malvina land, but his gambit was unsuccessful and the agents survived. Yrssk and the Children of the Tempest subsequently attacked the agents in the Steamfields, a geologically active region of Nyriaan, and he was defeated.