How to unlock: Complete the Dorian's Request operation and talk to Dorian.
Quest giver: Dorian (M12,4)
Complete the "Dorian's Request" operation available at the War Table. First, go to Hinterlands and kill two Venatori Mages.
One of them can be found north from the farms, in the top-right corner of the map (M3,45a). You will find the second target south-east from the campsite in the forest (M3,45b).
Go to Exalted Plains and you will find the last Venatori near the camp on the swamp (M18,19a). After killing the last one, you will complete the quest and gain Dorian's support.