Duras is the son of Ja'rod, Mogh's greatest rival. Named after his powerful house, he held a seat on the Klingon High Council by 2366. He led the cover-up of his father's treachery with the Romulans during the Khitomer Massacre that took place in 2346 and tampered with official records to make it look like Mogh had betrayed the 4,000 colonists of Khitomer even though he has died as well. Duras attempted to kill Kurn and Captain Picard to keep the truth from coming out, but he failed. The truth was still hidden to keep the empire from a civil war and Worf accepted discommendation to protect Duras.

A year later, Duras poisoned Council Leader K'mpec with radioactivity in order to become the new leader of the council. During the rights of succession aboard the Enterprise, Duras murdered K'Ehleyr when she began to find out the truth about the Khitomer Massacre. Worf killed him in revenge and that made his rival Gowron the only choice for the new leader of the empire. Six months later, Duras's sisters Lursa and B'Etor bid for the leadership of the council behind the bastard son of Duras, Toral.

Sources:
http://www.startrek.com/library/individ.asp?ID=71388