From Halopedia, the Halo wiki
At some point Capital-Enforcer had guarded a facility visited by the Librarian for three daily cycles. In the later years of the Forerunners' conflict with the Flood, Capital and several other Warrior-Servants were assigned to Seclusion Spiral, a gas mining station on the planet Seclusion. One day, while on patrol in Vane One with three other Forerunners; at some point one of his officers, Dutiful-Marcher, went missing, he contacted Adequate-Observer at the station's hub to alert everyone that they were under attack by the Flood.
Capital received reinforcements from the other patrols and engaged the Flood, when seemingly defeated, Dutiful-Marcher's Combat form released several Infection forms. Capital and his troops fell back and he ordered Adequate to close bulkhead one-stroke-four, temporarily sealing off the Flood. Capital eventually made it to the hub and sealed off Vanes One, Two, and Four to delay the Flood, his ancilla left a message that power to the transponders that relay messages between personnel was lost. Capital also intended to make a last stand in Vane Five, where he was eventually joined by Adequate-Observer, who informed him they were the only Forerunners left. Capital decided they had to scuttle the station, otherwise the station would become a trap for others. Needing both master keys to accomplish this, Capital gave his to Adequate and told him to scuttle it when the former fell. Soon after Adequate left Capital was turned into a Combat Form.
List of appearances