Who is Fouel, the Chou-Hoi from The Killing Zone: My Life in the Vietnam War and what is their importance?

Fouel, the Chou-Hoi, is a former Vietcong guerrilla who has been recruited by U.S. Intelligence. He and his military intelligence handler are flown to Lt. Downs' platoon twice to question and round up local Vietcong after a village is surrounded. Fouel is described as 5-feet tall and thin, like most Vietnamese that Lt. Downs sees. He is brutal with Vietcong, hitting them and being willing to torture them. Nevertheless, he and such Vietcong turncoats are not trusted by Lt. Downs and other American soldiers.