Toral is Duras' bastard son.
Following the death of Duras, his rival Gowron was assumed to be the sole candidate for Chancellor of the Klingon Empire until Toral appeared at Gowron's investiture, claiming to have inherited his father's right to the office. Several major Klingon families, allies of Duras and enemies of Gowron, decided to back Toral's claim, resulting in the Klingon Civil War.
Toral himself was nothing more than a figurehead for Duras's sisters, Lursa and Betor. He was captured as the war concluded, and Gowron bestowed the right to kill him on Worf, who had been greatly wronged by Duras before assisting Gowron in the war. Having seen enough senseless killing, Worf chose to spare Toral's life. What happened to him after that is unknown.