Gradak Kaz was a joined Trill Starfleet officer and penultimate host of the Kaz symbiont. Sometime in the 2370s, Gradak's wife had been killed by the experiments of the Cardassian scientist Crell Moset after the Cardassians attacked a Maquis base on Tevlik's Moon. Gradak would carry the bitterness of that loss the rest of his life, and even into his successor host.
Sometime later, a wounded Kaz was brought aboard a Federation starship. Too severely injured to be saved, Gradak died soon after, although the symbiont was successfully transplanted into a Trill medical officer named Jarem. (VOY - Spirit Walk novels: Old Wounds, Enemy of My Enemy)