The IKS Vorn was the Klingon Bird-of-Prey that carried Duras to the rite of succession in 2367, and aboard which Worf killed him in vengeance for the murder of K'Ehleyr.
The Vorn appears in the Next Generation episode Reunion. When the dying Chancellor K'mpec asks Picard to arbitrate the choice of his successor, the two claimants arrive to meet the Enterprise-D, Duras aboard the Vorn and Gowron aboard the Buruk.
A bomb goes off during the Sonchi ceremony on K'mpec's ship, and the device is shown to be of a Romulan type carried by one of Duras's men. K'Ehleyr then uncovers the truth about the Khitomer massacre and Duras kills her for it.
Worf claims the right of vengeance, beams to the Vorn and kills Duras in single combat with a bat'leth. The act leaves Gowron as the only candidate, and earns Worf a formal reprimand from Picard.