Duras

Duras was a power-hungry Klingon whose petty schemes led to the Klingon Civil War.

After poisoning K'mpec, Duras contested Gowron's claim to the Klingon Chancellorship and killed the half-human K'Ehleyr to cover up one of his crimes. K'Ehleyr's baby's daddy, Worf, then killed Duras.

Duras' sisters Lursa and B'Etor, who were secretly supported by the Romulans, revealed that Duras had a bastard, Toral, whose challenge of Gowron for the Chancellorship kicked off the Klingon Civil War.