A mercenary is one who fights for money. Armed groups of trained
soldiers who would hire themselves out were common in more
ancient times. Mercenaries could be either individuals or groups
of soldiers. As examples, Greek mercenaries were popular in
ancient times, fighting in various battles for the Persian
Empire while the Swiss made sought after mercenaries around the
1400's for the various battles in Europe. The Flying Tigers were
mercenary pilots who fought for China in the Second Sino-
Japanese War and were paid a bonus for every Japanese plane shot
down.