Related Rule
Russian Federation
Practice Relating to Rule 108. Mercenaries
Section A. Definition of mercenaries
The Russian Federation’s Regulations on the Application of IHL (2001) states:
mercenaries means persons specially recruited and taking a direct part in hostilities with the purpose of obtaining private gain. While doing so, they are neither nationals of a party to the conflict, nor residents of the territory controlled by a party to the conflict. Mercenaries are not members of the armed forces of the belligerent parties and they have not been sent by a state which is not a party to the conflict on official duty as members of its armed forces. Military instructors or advisers who have been officially sent by one state to another state in order to render assistance in the development of its armed forces shall not be considered mercenaries unless they take a direct part in hostilities. 
Russian Federation, Regulations on the Application of International Humanitarian Law by the Armed Forces of the Russian Federation, Ministry of Defence of the Russian Federation, Moscow, 8 August 2001, § 1.
The Russian Federation’s Criminal Code (1996) defines a mercenary as:
a person who acts for the purpose of getting a material reward and is not a citizen of the State that participates in the armed conflict or hostilities, who does not reside on a permanent basis on its territory, and who is not fulfilling official duties. 
Russian Federation, Criminal Code, 1996, Article 359, note.