Duras
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.[1]
Duras poisoned the Klingon Chancellor, K'mpec, to create an opportunity to move into the Chancellor's position.[2] 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.
After Duras' death, his sisters Lursa and B'Etor revealed that Duras had a bastard son, Toral, who challenged Gowron for the Chancellorship, instigating the Klingon Civil War.[3]