Thorpe was a member of the mercenary group Graham Directive Security.
Thorpe Worked with the Army in Gabon and spent time jailed in Mogadishu, Somalia and in Aydin, Turkey as well as in Peru. Thorpe recounts that the prisons were very unpleasant but says that it was nothing compared to what the Predators did. It is insinuated that they tortured him or abused him some way. Thorpe mentions that the Predators killed his commander and an Army captain and that they were lucky to have died quickly.
At some point in what could be assumed to be the 21st century, Thorpe was deployed to East Africa with Graham Directive Security to help defend American interest in the war-torn nation. During the mission a group of Predators decided to hunt the security force. Most of the force were killed by the Predators before an air lift could rescue the remaining members. Thorpe was last seen fighting the Predators after ordering his men to escape. By the next morning, Thorpe was missing and it was insinuated that he was killed.
However, it was later revealed that Thorpe survived and conveyed a testimony of the events which took place in East Africa. He later stated in a video log that he was held captive on a Predator ship for some time after the encounter. He also said that he believed their culture was based on killing and conquering. This is a somewhat inaccurate testimony on Predators as a whole since he was held by the rogue group of Killers, rather than the mainstream Hunter variety of Predators. After being held on the Yautja ship, for unexplained reasons, his captors dropped him off in the desert of the American Southwest before wandering in Cadiz, California.
Thorpe's statement was archived as "beyond top secret" until centuries later it was examined by the Colonial Marines to learn more about the Killer Predators.
Thorpe openly disrespects the authority of military personnel, preferring to trust his own experience and instincts. He is a hardened combatant who is rightfully confident of his skills. He is somewhat jaded and bitter, possibly from years of being exposed to violence. He reveals his hatred of the Predators later on in the series. Though there is one of them that appears to side with the humans he insists on distrusting them. He believes them to be barbaric.