Gatt is an elven agent of the Ben-Hassrath.
Gatt was a slave in Tevinter until he met Hissrad. The Qunari slew his masters and freed him, and he then joined the Qun, eventually being recruited to the Ben-Hassrath. Hissrad and Gatt had many missions together and became close friends, and after his friend started to work as captain of the Bull's Chargers mercenary company and many Ben-Hassrath agents suspected his desertion, Gatt tried to convince them they were wrong.
If the Inquisitor accepts Iron Bull's offer of an alliance with the Qunari, Gatt is sent as a representative to help Iron Bull cover a Qunari dreadnought that seeks to eliminate a group of Venatori trying to smuggle red lyrium.Should the Inquisitor choose to sacrifice the Qunari dreadnought, Gatt will visit them and Iron Bull in Skyhold to officially state that the Inquisition and its now tal-vashoth ally Iron Bull will not receive any more Ben-Hassrath reports or aid from the Qunari against Corypheus. However, if they choose to defend it and lose the Bull's Chargers, Gatt will bring the news of a full alliance and access to the Qunari spy network instead, declaring the inquisitor basalit-an.