In Star Trek VI: The Undiscovered Country, the Klingon chancellor assassinated at the start is Gorkon.
Gorkon is played by David Warner and leads the Klingon Empire during a major political crisis. After the moon Praxis is destroyed, the Klingons face an environmental and economic emergency. Gorkon recognizes that his empire can no longer sustain its long-standing confrontation with the United Federation of Planets.
He therefore seeks peace with the Federation and travels toward negotiations. The USS Enterprise is assigned to escort him, but Gorkon is attacked aboard his own ship and fatally wounded. His death threatens to derail the peace process and creates suspicion between the Klingons and Starfleet.
Gorkon is often confused with Azetbur, his daughter and successor. Azetbur becomes chancellor after his death and continues the negotiations. The film’s broader diplomatic story is distinct from the assassination itself, which is the event that drives the central mystery.