According to legend, Morath dishonored himself and his family by telling a lie and/or breaking his word. Kahless challenged him to battle but Morath was a coward and 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. (TNG: "New Ground", "Firstborn")
Again, according to legend, Morath murdered his father over a sword. As Kahless held their dead father, Morath threw the sword into the sea, saying, "If he could not possess it, neither would Kahless." This was the last time the two brothers spoke to each other. (TNG: "Birthright, Part II")
Michael Jan Friedman wrote in his novel Kahless that Morath was the driving force of the revolt against Molor. He also stated that the honorable one was Morath and not Kahless, who had been a petty bandit before meeting Morath. The book also states that Morath and Kahless only fought on and off for twelve days, and the fight was finished when Kahless admitted that he had lied and accepted the role of the leader of the revolt. It goes on to state that the clone of Kahless is in truth the clone of Morath.