Duras was a power-hungry Klingon whose petty schemes led to the Klingon Civil War. He came from a politically powerful Klingon family and held a seat on the Klingon High Council. His father, however, had committed treason by giving secret access codes to the Romulans, resulting in the massacre of a Klingon colony at Khitomer. To make the dishonor worse, which is perhaps why Duras endeavored so hard to keep it secret, his father made sure it looked like Worf's father had been the one to give up the codes.
Duras poisoned the Klingon Chancellor, K'mpec, to create an opportunity to move into the Chancellor's position. Duras contested with Gowron to claim the Chancellorship, and killed the half-human K'Ehleyr to cover up his family history. K'Ehleyr's baby's daddy, Worf, then killed Duras in a vengeance duel.