Grim is a laconic member of the Bull's Chargers.
According to Iron Bull, Grim is a lost king of a small country, or a chieftain.
During the first conversation between The Inquisitor and Iron Bull at Skyhold, the latter one invites the Inquisitor to come with him. The Qunari takes the Herald to a pair of new Inquisition recruits and introduces the Inquisitor as Grim. The Inquisitor then can pretend to be Grim by communicating through grunts, or break the character and speak at volume.
Demands of the Qun
Investigate Redcliffe Castle - Available after Champions of the Just
Investigate Therinfal Redoubt - Available after In Hushed Whispers
Hunt Therinfal Redoubt Demon - Complete Investigate Therinfal Redoubt with Leliana
Destroy Adamant Fortress - Available after Here Lies the Abyss
Meet Orlesian Mercenaries - Available after Wicked Eyes and Wicked Hearts
Inflate Inquisition Numbers - Available after What Pride Had Wrought