The IKS Negh'Var was a Klingon Negh'Var-type warship that was in service with the Klingon Defense Force in the late 24th century.
Launched in the early 2370s, it was the first Negh'Var warship in the fleet, and served as the flagship of the Klingon Empire. It was equipped with a cloaking device.
In early 2372, the Negh'Var led a task force consisting of hundreds Klingon vessels in an invasion of the Cardassian Union. It was commanded by General Martok (or rather the changeling infiltrator that replaced Martok). The vessel later led the attack on Deep Space 9. (DS9: "The Way of the Warrior")
In mid-2373, the Negh'Var, carrying Chancellor Gowron, retreated to Deep Space 9 along with other Klingon forces, which had been expelled from Cardassian space by the Dominion. (DS9: "By Inferno's Light")
When the starship was seen in "By Inferno's Light", it was not identified as the
Negh'Var in dialogue, but was mentioned in the script.
According to the script for the episode, the pronunciation for Negh'Var was "NEG-var". 
The Starships RPG sourcebook gives its registry as IKS-7500.