Kojo “Romeo” Agu was born on the outer colony world of Madrigal in 2524, escaping the glassing of the planet when he was only four. When he was old enough, Agu joined the Merchant Marines, and later the ODSTs after having an affair with the wife of the Governor of Castra, earning him the nickname Romeo. Romeo fought in many battles as an ODST in the later years of the war, including alongside Taylor “Dutch” Miles in Operation: FIRESIDE during the Battle of Ariel. In the final days of the war leading into the Battle for Earth, Romeo joined Alpha-Nine, replacing the many former members that Edward Buck had lost under his command previously. All of Alpha-Nine survived the war, continuing their service with the UNSC after the dissolution of the Covenant.
Alpha-Nine was put to work against insurrectionist forces in the months and years following the end of the Human-Covenant War, most notably on Draco III where they put down a URF rebellion at the cost of one of their own, the Rookie. At the end of that mission, Buck and the entire Alpha-Nine squad was approached by Jun-A266 to join the Spartan-IV program based on their exemplary performance. Though Dutch declined, Romeo, Buck, and Michael “Mickey” Crespo accepted, becoming three candidates in the second Spartan-IV class.
Following Spartan-IV training and augmentations, Alpha-Nine was re-instituted as a Spartan-IV fireteam, consisting of Buck, Romeo, and Mickey. This was short-lived however, as Mickey betrayed both Buck and Romeo after joining the United Rebel Front in 2555. Though both Buck and Romeo continued as Spartans following the incident, Buck eventually joined Fireteam Osiris and Romeo was reassigned to another Spartan fireteam. Following the Raising of the Guardians in 2558, Veronica Dare gave Buck a mission to reactivate Alpha-Nine, bringing all former members back together as a Spartan-IV fireteam, save the deceased Rookie.