A mercenary is a private individual who joins an armed conflict for personal profit, is otherwise an outsider to the conflict, and is not a member of any other official military. Mercenaries fight for money or other forms of payment rather than for political interests. Beginning in the 20th century, mercenaries have increasingly come to be seen as less entitled to protection by rules of war than non-mercenaries.
https://en.wikipedia.org/wiki/Mercenary