Captain Callum Armstrong, given the nickname Mini, by his soldiers, is a capable officer of the 1st Parachute Bridgage, the Red Devils. Callum was born to an American Immigrant and a Scottish Citizen, living in Liverpool. His father at one point had served in the US Army, leaving as a Sergeant, and eventually getting a job in the foreign land of the United Kingdom. Due to this, Callum was considered a naturalized citizen of the UK, alongside having citizenship for the US. He lived there for many years, living his younger years out as a bit of a troublemaker. He'd get into fights, and other such matters, consistently when he was young. However, this was due to some sense of justice he had, following his moral code, to do what was best for him and for people he cared for. This carried on throughout secondary school. He eventually decided that he wished to attend RMA Sandhurst, with the goal of joining of joining the British Military.

His attendance at Sandhurst was met with some opposition from his mother, who was a doctor, not wanting to see her son get into any trouble. However, he, with his still very American accent, left home with the goal of becoming an officer. He did exceptionally in the Regular Commissioning Course, earning a Sword of Honor and the Queen's Medal. When he eventually left, at the ripe age of 19, he had the distinct goal of joining the paratroopers. He did exceptionally in his POIC and was brought on as a Second Lieutenant in the Paratroopers.

From there, he served his time, working exceptionally in his duties, being deployed all across the world. In one specific instance, in 2016, he was deployed alongside US Paratroopers for a joint operation during the War on Terror. It was his exceptional abilities and performance during this mission that earned him both a promotion to Captain, and the opportunity to work with US Forces in the future. He was eventually offered the oppurtunity to work as a Foreign Attaché as a Member of NATO, to work with the 2nd Cavalry Regiment of the US Army. He never had any specific loyalties to the US Army during his Service, and his subsequent deployment alongside them. He eventually found himself working very closely with a 1st Lieutenant James Reverend of the 5th Platoon of Bull Troop, acting as an Advisory Factor. They were some of the few remaining officers after the virus spread.

As they were approaching the Airport and heard the chatter of the horrific sounds, Callum knew that it was too late. Soon enough, they all left and returned to Rena Camp, him being one of the few remaining survivors. As more and more people deserted, Callum knew he would not likely see his home anytime soon. He took what he could hold and left, starting on his own path. He had a future to uphold. He walked on out of there, taking what he could, no specific path for him, just a goal to survive, and perhaps, find someone to shack up with in this disheveled world.