Slau Dha is an Eldar Autarch and member of the mysterious Xenos organization known as Cabal. One of the most visible faces of the Cabal, Slau Dha is the one who gave John Grammaticus his offer to become a Perpetual and then recruited him as an agent for the Cabal. Despite this, Slau Dha holds humanity in low regard and commonly referred to them with the derisive term mon-keigh. He is also apparently one of the organizations most violent and militant members, but was extremely loyal to its cause. This loyalty made the Autarch sneak members of the Cabal into the Black Library, where they learned of the coming of the Horus Heresy; which allowed them to begin trying to shape the Imperium's impending civil war to their advantage.
Later when Eldrad Ulthran began eliminating members of the Cabal over fears their plans will bring the galaxy to ruin, Slau Dha was among the last of its members to be targeted. Eldrad and his agent Barthusa Narek infiltrated Slau Dha's palace on an unknown world, ambushing him when he was alone. Slau Dha condemned Eldrad as a traitor to the Eldar race before summoning a force of Harlequins. After a brutal battle Slau Dha was slain, though Eldrad was wounded in the process.