Mordirith, the False King, is the Steward of Angmar and one of the primary antagonists of The Shadows of Angmar. While the Witch-king of Angmar is abroad to seek the One Ring, Mordirith commands the forces of Angmar in his stead. This position leads him into direct battles with the heroes of Eriador on several occasions. Most notably, he can be found as the final boss in the last room of the Castle of Carn Dûm, called the Seat of the Witch King.
Mordirith was once Eärnur, the last king of Gondor who routed the Witch-King's army at Fornost in III 1974. The Witch-king challenged him in III 2050 and Eärnur rode to Minas Morgul but was never heard from again. The Nine defeated him in battle and he became a Cargul. The Witch-king bound his spirit and gave him great power, making him Steward of Angmar and the Witch-king's most faithful servant.
After his defeat at the hands of Narmeleth, Mordirith is sent back to Minas Morgul, receiving yet another, strong body from his master. He now leads the Morgul-host in the conquest of Osgiliath and the siege of Minas Tirith under a new name - Gothmog, the Dread Terror of Minas Morgul.
Players battle against Mordirith in a number of forms and places. These include:
- Mordirith (The Gates of Carn Dûm)
- Mordirith (Mordirith's Fall)
- Mordirith (Carn Dûm)
- Mordirith (Gador Gúlaran)
- Gothmog (The Darkest Hour)
- Gothmog (Throne of the Dread Terror)
-  Volume I, Book 7, Instance: The Gates of Carn Dûm
-  Volume I, Book 8, Instance: Mordirith's Fall
-  Volume I, Book 11, Instance: Prisoner of the Free Peoples - Solo-only
-  Volume I, Book 14, Instance: The Doom of the North
-  Volume I, Book 15, Instance: One Hope Remains
-  The Battle of Rhunendin - Fellowship
-  Volume IV, Book 3, Instance: Gothmog Appears
-  Volume IV, Book 6, Instance: On a Field of Red
In addition, the player visually remembers Mordirith in:
-  Volume III, Book 6, Instance: Troubled Dreams - Solo-only
-  Volume III, Book 7, Instance: A Journey by Boat - Solo-only
- "Let us put it to the test and see who is the stronger!"
- "I would not thought it possible that you could challenge me for so long..."
- "Let our battle be at its end!"
- "I am Gothmog, the Dread Terror, and Minas Tirith shall crumble before me!"