Date of birth:
|Political and military information|
Nicknamed "The Mark" by his fellow Spartans due to his marksmanship abilities, Petty Officer Third Class Mark is proficient with numerous sniper rifles, including the SRS99C-S2 AM. He is also skilled with an MA5 Series assault rifle. Mark fought in the Battle of Onyx,  which he survived because Lieutenant Commander Kurt Ambrose ordered him through the slipspace portal in Onyx's core which led to a shield world.
Mark was conscripted into the Gamma Company of the SPARTAN-III program, initiated around 2546. Conscripts were between the ages of 5 and 7 when he, along with other orphans volunteered to become Spartans and avenge his family and home planet.
 Battle of Onyx
 Zone 67
Mark was assigned to Team Saber, under the command of Private Ash-G099. When the human forces on Onyx came under attack by Sentinels, the teams were still vying for top honors. Team Saber went dangerously close to Zone 67 to avoid the other teams. The team spied what they assumed at the time to be a new kind of Covenant drone due to its energy shields. They decided to investigate and the Sentinels engaged. Mark remained with the team as they tried to figure out the weak spots of the drones. He and the rest of the team hurled rocks at the drones and to their surprise, the drone's shields did not activate. The Sentinel chased Ash into a hole and Mark and the rest of the team pummeled the drone with huge rocks, destroying it.
A general decision was made and the Team moved to the armory to get heavier armaments. Team Saber met up with Commander Ambrose, Chief Mendez, as well as PO2 Tom and Lucy; and proceeded to play life and death games of cat and mouse with the sentinels. Mark and the team later met up with PO2 Kelly-087 and Dr. Catherine Halsey and were subsequently engaged by a pair of Sentinels. After the skirmish, Mark and the rest of the Spartans took Dr. Halsey and Kelly to a bombed out bunker where Halsey revealed the origin of the Sentinels and what to do next.
 Team Katana
After the team destroyed the two Sentinels and the overwatch position at Camp Currahee, they moved back to Zone 67. After making their way through an excavated Forerunner city, they discovered Onyx's map room, where they learned that Onyx was an artificial construct, as well as pinpointing the location of Team Katana. Before recovering Team Katana, however, AI Endless Summer sent them on a mission in a Sentinel manufacturing facility and make sure no more Sentinels were produced. Mark and Team Saber played a key role in destroying the factory, using its teleportation grid to their advantage. Later, they moved out to discover Team Katana and found them in slipspace field pods. However, the Covenant knew the location of the two teams and were advancing towards their position with four legions of Sangheili, Mgalekgolo, and other soldiers, as well as armored vehicles.
 End of the battle
The humans fell back to a portal which led to Onyx's interior shield world, located within a massive room in Onyx's core, where they soon found themselves surrounded by the Covenant. Mark and the other Spartans formed a loose half-circle "killzone" around the portal and picked off targets at close and long range. They managed to defend the entrance to the shield, although it had come at some serious losses.
PO2 William-043, PO3 Dante-G188, and PO3 Holly-G003 had already been killed by the advancing Covenant army. Due to little time left, Commander Ambrose ordered Team Saber through the portal before it closed. Soon after, Dr. Halsey and the surviving Spartans entered the portal. On the other side of the rift, Mark awaited Kurt's arrival, but he never came, instead Kurt gave his life by detonating a FENRIS nuclear warhead. The blast killed Fleet Master Voro Nar 'Mantakree and all of his forces.
 Shield world and later career
Once Mark, Dr. Halsey, and the other Spartans were safely inside the Dyson sphere that lay beyond the portal, they made gravestones for LCDR Kurt Ambrose-051, P02 William-043, PO3 Dante-G188, and PO3 Holly-G003. After the ceremony, Mark and the other SPARTAN-III's were reassigned to SPARTAN-II Blue Team by Lieutenant, Junior Grade Frederic-104 and Petty Officer Second Class Kelly-087.
Mark and the other survivors then proceeded to explore the vast construct, soon establishing base camp in a Forerunner structure. A group of Huragok, discovered by Lucy-B091, eventually helped them bring the sphere out of its slipspace bubble into normal space, and an ONI team was dispatched to retrieve them. The few days the survivors had stayed inside the slipspace bubble turned out to equal over three months in normal space-time, and as such they returned to normal space in February 2553.
Mark and the others were taken to Earth aboard the UNSC Port Stanley for a debriefing in HIGHCOM Facility Bravo-6 in Sydney. He and the other surviving SPARTAN-IIIs were later offered the chance to integrate into the SPARTAN-IV Program under the leadership of the surviving SPARTAN-IIs.
 List of appearances
- ^ Halo: Ghosts of Onyx, page 100
- ^ a b Halo: Ghosts of Onyx, page 383
- ^ Halo: Ghosts of Onyx, page 116
- ^ Halo: Ghosts of Onyx, page 356
- ^ Halo: Ghosts of Onyx, page 365
- ^ Halo: Ghosts of Onyx, page 117-119
- ^ Halo: Ghosts of Onyx, page 130-135
- ^ Halo: Ghosts of Onyx, page 170-176
- ^ Halo: Ghosts of Onyx, pages 313-324
- ^ Halo: Ghosts of Onyx, pages 341-343
- ^ a b Halo: Ghosts of Onyx, pages 360-372
- ^ Halo: Ghosts of Onyx, page 378
- ^ Halo: Glasslands, page 382-389
- ^ Halo: Glasslands, page 401
- ^ Halo: Glasslands, page 435