The Grim Disciples is a non-playable rift faction for the Defiants. Notoriety can be earned with them by closing death rifts, defeating invasions and footholds, and slaying mobs from death rifts, invasions, or footholds.
The quartermaster for The Grim Disciples is Jorostir Kios, who can be found in Meridian in the College of Planar Studies.