Middle-earth™: Shadow of War™

To unlock this achievement you need to defeat the Lawless.
The Lawless is an Orc that appears after you have completed all of the "Fallen Blades" quests to collect all of the Elven gear. Once you have completed all six of the Fallen Blades missions in each region, a new mission called 'The Lawless' will appear in Gorgoroth. Head there and complete it to unlock this achievement.