Sergeant Gaines was a Sentinel who took part in Operation Iron Fist and was part of the SAR team under 2nd Lt. Nathan Hale. Gaines was most probably picked for the mission because of his height which meant he could spot Chimeran ambushes from far away. After they recovered the Alpha Tech they were looking for they headed for the Landing Zone on top of the facility. But on the way they encountered Hybrids on the way in which one of them leaped at Gaines, who he shot it and killing it instantly; however, the corpse carried on forward until its teeth sank into Gaines' neck and killing him instantly.