Grayson MacMillan was a former "child soldier" of the Insurrection turned mercenary, who came into prominence during the post Human-Covenant war period. Trained to be an explosives expert since the age of six, Gray defected from the Insurrection when he turned twenty years old. During his reign he became one of the most efficient and prominent explosives and ordinance experts the criminal underworld has ever known. These dangerous habits combined with a thirst for glory makes Grayson a formidable but slightly unstable asset on the field of battle.
Gray was born right in the middle of the Human-Covenant war, in 2544. The Insurrectionists took the Covenant's attack on the UNSC as an opening to strike, forcing them to fight a war on two fronts - one with the "Innies", and others with the religious aliens. At eight years old, Gray was being trained as a child soldier during 2552. He needed these skills to survive, as the Insurrectionists had gone underground due to the raging conflict. Not much else was revealed about what Gray did as a child soldier, despite first displaying his affinity for explosives.
"What do you mean he's "unstoppable"?! He's ONE man armed with a few grenades! Take! HIM! DOWN!"
―The last words of an Insurrectionist leader, shortly before death by explosion.
Much later, in the heat of 2564, Gray was being treated as expendable. Commonly sent on suicide missions and surviving, the Innies thought Gray had used up his potential. Soon, he hatched a plan - he would raid the armory holding enormous amounts of weaponry acquired from the Black Market. Due to the Innies ceasing their operations during the Human-Covenant War, they had acquired an embarrassing amount of firepower from both sides, UNSC and Covenant. He got to work on constructing his own personal helmet from scavenged MJOLNIR parts and acquired a Type 25 Grenade Launcher - commonly known as the Brute Shot -, an M319 IGL, MA37 with underbarrel grenade launcher several grenades and one his signature weapons, his tomahawk. With such explosive potential at his hands, he immediately began bombarding the Insurrectionist compound he had called home for the last ten years. Laying waste to the rebels, he scavenged what money, food and water he could and was discovered by a traveling drug cartel who had arrived on Earth. Although held at gunpoint, the Insurrectionist offered Grayson to sell his skills to the cartel as a bodyguard. The cartel's members decided to take him in under their wing.
Drug cartel service
Years past as Grayson eventually settled into the cartel's service. Working his way up the criminal totem pole was no small feat, but Grayson proved himself to succeed almost every time. Of note was one of his first missions aboard a UNSC freighter, where they stole a large shipment of medical supplies. The entire team on board died except for Grayson due to the presence of Marine Corpsmen on the ship. Their only disadvantage was the mercenary with the one weapon which could fire around corners and bounce off the nearby walls. Grayson did not even need to see the enemy to eliminate them.
Eventually, MacMillan rose high enough that he became their quartermaster, overseeing all their weaponry.
Galaxy-weary and battle-hardened, Grayson's love for explosive weaponry is only matched by his determination and combat expertise. Although somewhat inept in some areas thanks to his lack of education, his fair share of experiences have helped him cope with the difficulties he'd experienced over the years. Never the less, his colored view of life is counterbalanced by his fun-loving glory hound side, often doing jobs for not just the money, but also the thrill of battle.