soldier of fortune 
noun
A person who works as a soldier for any country or group that will pay them; a mercenary: he had fought with soldiers of fortune in South Africa, Chad, and Lebanon...
- Their principal commanders were Gustave-Paul Cluseret, a revolutionary soldier of fortune, and Louis Rossel, a young officer; they were aided by several former Polish and French army officers, notably Jaroslav Dombrowski.
- Swiss soldier of fortune, Colonel Henry Bouquet, was en route from his headquarters in Philadelphia to relieve Fort Pitt during the time period in question.
- He had fought with the Abraham Lincoln Brigade during the Spanish civil war, later becoming a soldier of fortune.