According to a CIA internal memo dated November 29, 1975, Zapata Petroleum began in 1953 through Bush's joint efforts with Thomas J. Devine, a CIA staffer who had resigned his agency position that same year to go into private business, but who continued to work for the CIA under commercial cover. Devine would later accompany Bush to Vietnam in late 1967 as a "cleared and witting commercial asset" of the agency, acted as his informal foreign affairs advisor, and had a close relationship with him through 1975.