I must protest. To offer the Klingons a safe haven within Federation space is suicide. Klingons would become the alien trash of the galaxy. And if we dismantle the fleet, we'd be defenceless before an aggressive species with a foothold on our territory. The opportunity here is to bring them to their knees. Then we'll be in a far better position to dictate terms.
~ Cartwright's rant on peace with the Klingons.
Admiral Cartwright is a supporting antagonist of Star Trek VI: The Undiscovered Country. As an Admiral he served as Commander-In-Chief, Starfleet Command. In addition he was the Starfleet liaison to the Diplomatic Corps.
He was portrayed by Brock Peters, who was best known for playing Tom Robinson in To Kill a Mockingbird as well as Benjamin Sisko's father Joseph Sisko in Star Trek: Deep Space Nine.
In the 2260s Cartwright was a Starfleet Captain, and commanded the USS Ark Royal. By 2268 Cartwright was a Rear Admiral working with Section 31. He ordered Captain Kirk and Mr. Spock to retrieve a Romulan cloaking device. Even back then Kirk was suspicious of the Admiral having a secret agenda.
In 2286 Cartwright led Starfleet's response when an alien probe looking for humpback whales began causing severe climatic disruption on Earth.
After the destruction of Praxis in 2293, the Klingon Empire sued for peace. Cartwright was a vocal opponent of the peace process, wanting to attack the Klingons, defeat them, and dictate terms. However Starfleet and the Federation Council did not accept his recommendations and supported the peace process.
Cartwright then got in touch with other members of Starfleet who felt as he did - including young Lieutenant Valeris, along with people in the Klingon and Romulan Empires who stood to lose if hostilities ended. Because Kirk had voiced support for some of Cartwright's positions, Cartwright and his co-conspirators used Kirk as a scapegoat when they assassinated the Chancellor of the Klingon Empire. They framed Captain Kirk and Doctor McCoy for killing Gorkon, and planned to assassinate the Federation President - an act they intended to blame on the Klingon Empire. Ironically, Kirk's battle prowess had the conspirators ask the Federation President for permission to stage a rescue mission, reasoning they would need Kirk once the war began. But the President rejected this as well.
However Kirk and McCoy were able to escape from Rura Penthe. With help from Captain Sulu of the USS Excelsior, the crew of the Enterprise arrived in time to the renewed peace talks to prevent the assassination. Cartwright attempted to flee but was arrested by Sulu and an Excelsior security team.
Cartwright was convicted for his role in the conspiracy and sent to prison. He died in prison in 2298 of apparent natural causes. Some members of Starfleet thought one of Cartwright's many enemies arranged for him to be killed in a way that appeared to be natural. As a result of his death by 2300 Valeris was the only known survivor of the conspiracy.
The script gave Cartwright's first name as Donald. Other licensed media gave Cartwright's first name as Lance.