Morath was a Klingon mytho-historical figure, the brother of Kahless the Unforgettable. According to legend, Morath dishonored himself and his family by telling a lie. Kahless challenged him to battle, but being a coward, Morath fled. Kahless pursued him across valleys and over mountains, to the edge of the sea. There, Kahless fought Morath for twelve days and twelve nights, until Morath was killed. (TNG: "Firstborn")
However, later Kahless descended into Gre'thor to redeem Morath and bring him to Sto-vo-kor. (VGR: "Barge of the Dead")