From Halopedia, the Halo wiki
Private Riley was an infantryman in the UNSC Marine Corps. He was part of Fireteam Charlie along with Private Kappus, Private Bisenti, Private Manuel Mendoza, Private First Class Wallace A. Jenkins, and Private First Class Chips Dubbo. His squad leader was then-Staff Sergeant Avery Junior Johnson.
Riley was the first recorded human successfully infected by a Pod infector during the Battle of Installation 04. When he was attacked by the creature during the raid on the supposed Covenant weapons cache, Private Kappus attempted to pull it off of him. Even though the Pod infector was soon removed by Kappus, another soon found him and turned him into a combat form.
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