In the IMC command structure, Vice Admiral Marcus Graves is formally known as the CINCFRONT, or Commander-in-Chief, Frontier Command.
Despite the elaborate title, Frontier operations are notorious for their lack of adherence to traditional protocol, allowing Graves to personally command IMC forces in the field, and to operate far more informally than commanders in the Core Systems. Graves has a reputation as a maverick within the IMC. His calls for policy change have often been deemed too risky to IMC forces, and too lenient to Frontier citizens. During the inquiry into the Odyssey scandal, Graves maintained that the ship was forcibly commandeered by MacAllan and his band of mutineers.
In the fifteen years following the alleged mutiny of the IMS Odyssey, Graves would go on to become Vice Admiral in command of the IMC forces in The Frontier, with Sergeant Blisk in charge of mission status and troop deployment and Spyglass being responsible for intelligence and Titan management for the pilots in the field.
The battle on the Frontier began changing upon The Refueling Raid launched by the Frontier Militia at Fracture. Graves ordered IMC pilots to get defense turrets up and running to prevent the Militia from gaining access to the fuel. During combat, the Militia flagship, the Redeye was heavily damaged by the turrets, but ultimately the Militia succeeded in getting the fuel they needed. After the battle, Graves asked Sergeant Blisk how many ships the Militia lost, and then inquiring how many were civilians. Graves expressed disappointment upon Blisk's dismissal that there was a difference between civilian and combatant within the Militia. Spyglass then informed the Vice Admiral that there was an unmarked colony nearby, and that it could be a Militia base. Graves ordered Blisk to send a small force to investigate, however Blisk used the civilians as targets to evaluate the new Spectre troops the IMC had received. Blisk then ordered IMC forces en masse to kill the Militia soldiers responding to the distress call the colony sent out. During the battle at The Colony, it was revealed that the planet was the final resting place of the IMS Odyssey, and that the colony had been founded by James MacAllan, who Graves had believed to be a dead man. Graves ordered MacAllan to be captured on charges of mutiny and treason, however the Militia requested Graves' old friend to become their leader. MacAllan agreed to do so if the Militia could evacuate the colonists. Upon doing so, MacAllan ordered the Militia support his efforts in retrieving information from the wrecked Odyssey's databanks. Graves ordered his forces to stop MacAllan's salvage of information from The Odyssey, however they failed to do so. Graves knew MacAllan's next move, leaving the relic behind in order to find Robert "Barker" Taube. Through informants, Graves learned Barker was in Angel City, and ordered search parties to find MacAllan's old wingman. IMC forces engaged Militia troops during Get Barker, attempting to find MacAllan and Barker, while the Militia snuck Barker out through the sewers. Graves requested reinforcements, which arrived in the form of the IMS Sentinel. MacAllan ordered the Militia to attack the Sentinel to force it to go to dry dock for repairs. The damage done to the ship by the Militia Hornet fighters did force the Sentinel to go to Outpost 207 for repairs. Graves was forced to scramble forces to defend the facility when the Militia launched an Assault on the Sentinel, however the IMC lost the vessel.
Graves also knew MacAllan's plan needed information on the repulser towers which protected the airbases in the Demeter system which in turn protected the refueling facility on Demeter itself. To do this, the Militia needed to go to Base Golden, an abandoned facility at the Boneyard on the planet Leviathan, where Barker used to be stationed. Graves ordered his troops to destroy the facility before the Militia could study the tower there, however the demolition was completed immediately after the Militia gained the information they required. Graves immediately ordered his forces to defend The Three Towers at Airbase Sierra, which were destroyed by the Militia, and caused the wildlife to cause the facility's devastation. During The Battle of Demeter, Graves directed operations from orbit while Blisk chased MacAllan as he planned to overload the main reactor and destroy the refueling base. Graves ordered Blisk to use hand to hand combat so to not damage the reactor's systems and do MacAllan's job for him. Graves realized that it was pointless once MacAllan locked himself in the reactor core and ordered Blisk to return to the fleet. Graves then sent evacuation craft for the pilots once the reactor began to go critical, however Spyglass cancelled the order and forced the fleet to jump to a safe distance to Graves's shock and frustration. MacAllan pleaded with Graves to take over for him as leader of the Militia, the same chance Graves gave him fifteen years before on the Odyssey before the reactor exploded. Graves could only watch in horror as Demeter was destroyed.
Three months following Demeter, Graves became Field Commander of the Militia forces and ordered the strike at the Hammond Robotics Spectre production facility. During the skirmish, Graves contacted Blisk, now a Commander under instruction from Spyglass who was Graves' successor as Vice Admiral. During the conversation, Graves implored Blisk to leave the IMC and join together, to fight the machines which made up most of the IMC's forces. Blisk retorts Graves' comment about the robots' loyalty lying with their operator, telling Graves he had no right to talk about loyalty due to his defection. Blisk then rejected Graves' words about the Militia being able to come out as victorious agains the IMC's machines and mercenaries, stating that he would fight Graves for nothing before terminating the connection. Graves laments his inability to reason with Blisk.
- Marcus Graves was voiced by Nathan Constance