The Marine was a guard stationed at Primerdyne R&D when an experiment went awry, unleashing an Interdimensional Horror into the facility. His gun having jammed, the Marine chose to flee in an escape pod, abandoning the scientists and his fellow guardsmen on board the station to their doom.
If the Bullet That Can Kill The Past is used on The Marine, he will be brought back to Primerdyne R&D before he left for the escape pods. Talking to an injured scientist outside the starting room will reveal that there was an issue during a test and "something" has come through a dimensional opening. The scientist says that the escape pods are just down the hall and advises The Marine to leave. If the Marine goes left and then up towards the Lab he will enter to see that other soldiers have taken cover in the room's lower corners. Suddenly, the Interdimensional Horror will emerge from a portal in the center of the room. If The Marine is able to defeat the Interdimensional Horror, he will be thanked by his fellow soldiers for saving all their lives (except the scientist in the hallway, as he has "definitely died") and honored as a hero.
Compared to the other standard Gungeoneers, the Marine has the least variance in playstyle and is relatively reliable in performance. He comes equipped with a piece of armor, which makes him slightly more durable than the rest of the characters. His starting weapon, the Marine Sidearm, has a high clip size and fire rate combined with decent damage output and comparatively high accuracy with a quick reload, making it a viable weapon by itself for the entirety of the first floor and a useful backup even beyond.
Military Training provides a notable increase in accuracy and decrease in reload times; provided the player can find weaponry to lend the trait to, it can vastly extend the effective range of some weapons and make some of the slower weapons more viable, particularly powerful bolt-action weapons such as the Hexagun. The increased accuracy can also make most shotguns much more effective at medium to long range, though it is recommended to stick to wider targets at these ranges nonetheless.
Supply Drop, if kept until required, is a guaranteed ammo drop in emergencies if the player is low on ammo. The downside is that the player is unlikely to need it until later floors; often, a better active item will drop beforehand and the player will be compelled to drop it or use it immediately. However, more experienced players who are using elevator skips to later floors, particularly the third or beyond, may find the Supply Drop highly useful. It may also be sold to the Sell Creep if one is strapped for casings.
Overall, The Marine is an extremely reliable character for combat, but while he receives a bonus to his gunplay, he lacks the special bonuses of other Gungeoneers, such as The Hunter's Dog or the variety of boosts The Pilot receives. However, he remains a highly useful character for players with a steady aim, as his sidearm is easily the most powerful of the standard infinite-ammo weapons and his passive gives him an almost alarming propensity for chewing through rooms with some weapons. He is best used if the player is looking to simply blast their way through the Gungeon, as other characters have bonuses that will help them with quests more.
- Nicknames that NPCs refer to The Marine as include:
- Tough Guy
- The alternate costume for the Marine is possibly a reference to both Black Iron Armor set and Solaire of Astora in Dark Souls.
- If the Marine loses his armor, his helmet will disappear. His helmet will reappear upon picking up armor.
- Furthermore, the Marine's starting armor is represented by his helmet during character selection, despite technically not being an item or a gun.
- The Marine's boss screen portrait might be a reference to DOOM's cover art.
- The Marine's portrait weapon is a close homage to the Pulse Rifle from Aliens.
- When the Marine faces left, the scar on his right eye will change to his left as the sprite is flipped.
- The Marine's past and appearance are based on the DOOM series.
- In the pre-alpha, the Marine was called the Soldier.
- If in co-op during the past, the soldier in the ending cutscene will say “We're all still alive because of you... and your... little friend?”
- Posters of Black Stache appear on certain walls in the marine's past.
- The Marine was considered for Indie Pogo as a Bullet Kin clone, but he was scrapped.
- The Marine makes an appearance as a costume in Heave Ho.