Slar was a Gorn slavemaster of the Tholian Assembly. He was the headmaster of the salvage team assigned to strip the USS Defiant. Essentially the leader over a specific slave group, Slar's orders were to gut the mirror universe starship. But during the gutting of the ship, it was boarded by invading forces from the ISS Enterprise of the Terran Empire.
Slar was the master of seven slaves assigned to disassemble the Defiant. When the Defiant escaped the Tholian spacedock, Slar began killing several of the Terran crewmembers, including Kelby, and stole several key components of the warp engines. Slar contacted Jonathan Archer, demanding a shuttlecraft to leave the ship. Archer refused, saying it was not a negotiation.
Slar was killed in an ensuing battle against Archer in a corridor of the Defiant. Archer had T'Pol increase the polarity of the gravity plating in the corridor, forcing Slar to the ground under an increased gravitational force. Archer then shot Slar several times with a phase rifle, effectively dealing with an unfortunate setback. (ENT: "In a Mirror, Darkly")