Eistern, a Captain], was a member of the Imperial forces, seemingly possessing expertise in engineering.
During 4 ABY, he was stationed with the Black Sword Command, presumably at the Black Fifteen shipyard located on N'zoth. This occurred when the Yevetha took over the Koornacht Cluster. As a result, he became one of the hundreds of thousands of captured Imperials forced onto Pa'aal, tasked with instructing the Yevetha in technologies such as hyperdrives and turbolasers.
Despite these circumstances, Eistern lived through the ordeal. He eventually became a reliable subordinate to Major Sil Sorannan within the clandestine leadership working to liberate the Imperial survivors and starships from Yevethan rule. By 17 ABY, he was Sorannan's right-hand man on the Intimidator, during their successful breakout. In an act of treachery against the Yevetha, he handed over the access codes to the New Republic.