Underlord Marcus is a rival Underlord in War for the Overworld. He appears in Campaign mode and as an AI personality in Skirmish and Multiplayer modes.
In Campaign mode, Marcus is a cowardly traitor who flees from his realm into Kairos, and makes a deal with the Empire for his own protection. In exchange for this, he guards the third Inhibitor, preventing Oberon from progressing into the mainland of Kairos.
Mendichaus expresses great distaste for Marcus, and his behavior, and urges Oberon to eliminate him for his betrayal. He is eliminated, along with the third Inhibitor, in Level 4 of the Campaign.
In Campaign mode, Marcus does not make any effort to expand, alter, or repair his dungeon, and it appears that he has had a fair bit of time here to prepare already. He is meant more as a training AI for other Underlords later on rather than an actual opponent. When an assault is made against him, he will rally all troops to the first threat he sees, leaving other routes wide open. He will occasionally use lightning, though not very effectively, and he does not heal his minions often. He makes little effort to engage the player when not in immediate danger, and his workers do not usually stray far from home.
- Marcus's dungeon theme in Campaign mode is the Sovriegn theme. It was unlocked by players who purchase the game's Underlord Edition.
- His colour in the campaign is Cyan.