Simcox, call-sign Bull, is a U.S. Marine.
Through unknown circumstances, Simcox joined the United States Marine Corps, where he gained the call-sign Bull.
In the early hours of October 25th 2003, Bull was among the Marines under Shane Schofield's command that were dispatched to assist two Delta teams fighting Chechen terrorists at a former Soviet base known as Krask-8.
Soon after they arrived at Krask-8, Schofield sent Bull to lead a small team to investigate the facility's office tower for signs of the Delta forces, since they had heard from them or seen any sign of the terrorists. Bull's team soon found the Delta force team led by Gregory Farrell, and Bull reported the deaths of the Delta men to Schofield, noting the disturbing beheading of Farrell. Moments later, Bull and the others were ambushed by the mercenary group Executive Solutions, and Bull attempted to radio Schofield for help, but soon he ended up being killed.