Slaughter

Slaughter was a NightWing guard, and the cousin of Vengeance. He was killed by Deathbringer as part of a deal.

Assassin

Quickstrike made a deal with Princess Greatness and Morrowseer. If her son Deathbringer could kill Slaughter or Vengeance, he could go to the continent with her.

Deathbringer decided immediately to kill Slaughter, because killing Vengeance was too risky. While Slaughter slept, Deathbringer crept up on him and prepared to kill Slaughter. However, Morrowseer woke him up an immediately warned him of the incoming assassination attempt. Deathbringer still managed to sneak up and kill Slaughter.

Though it was his job, Deathbringer still felt remorse for killing a fellow NightWing.

Slaughter's murder most likely caused the rivalry between Deathbringer and Vengence.