During Act 2 you can start to dominate Orcs.
Pick any fortress and find a Warchief with at least two Bodyguards.
Find the bodyguards and dominate them. On the second city you go to during this act you can send them to become spies after dominating by pressing
. Do this for all bodyguards and a new mission called "betrayal" will spawn. Complete this to unlock the achievement.
If the weakest Warchief doesn't have any bodyguards, go to "Army" and select a warchief. Press
to command and then hover over the Warchief and press
. This'll set up a new mission for the fighting pitt. If you're Captain is successful, he'll become the warchiefs bodyguard (spy for you).