A spy for a foreign country WordNet 3.0 & Open English WordNet

A foreign agent is any person or entity actively carrying out the interests of a foreign principal while located in another host country, generally outside the protections offered to those working in their official capacity for a diplomatic mission. Wikipedia

A person who carries out the interests of a foreign country Wikipedia Disambiguation

Person who carries out the interests of a foreign country. Wikipedia Disambiguation

Anyone who actively carries out the interests of a foreign country while located in another host country. Wiktionary