Duras

As the son of Ja'rod, the greatest rival of Worf's father Mogh, Duras was his powerful house's namesake and representative on the Klingon High Council by 2366 and led the cover-up of his father's treachery in the Romulan massacre of the Khitomer outpost 20 years earlier. Tampering with captured records as 'new evidence,' he blamed Mogh in an elaborate cover-up as the one behind the debacle in which Worf's parents were among 4,000 colonists killed ironically, tainting Mogh's survivor with his alleged dishonor. Despite Duras' best efforts via assassins and manipulation, the truth was realized but kept hidden to preserve the political status quo and avoid civil war.

He nearly became chancellor of the empire a year later when he dishonorably poisoned Council Leader K'mpec to get the job, but he was killed by a raging Worf in combat after Duras murdered Worf's mate K'Ehleyr when she began unraveling the truth about Khitomer. Duras' death sealed the choice of rival Gowron as new leader of the empire, although Duras's sisters Lursa and B'Etor turned up six months later to bid for the leadership behind Duras' bastard son, Toral, and spark a civil war after all.