A mercenary is a professional soldier who fights for money rather than loyalty to a country or cause. Unlike regular soldiers who serve their own nation, mercenaries will fight for whoever pays them.

Throughout history, mercenaries have played major roles in warfare. In medieval Europe, Swiss mercenaries were famous for their discipline and skill. Italian city-states hired condottieri (mercenary captains) to lead their armies. During the American Revolution, German soldiers from Hesse, often called Hessians, were hired by Britain to fight the colonists.

The word carries a negative connotation beyond just military contexts. When you call someone mercenary, you mean they care only about money and personal gain, not about doing what's right. A mercenary attitude means putting profit above everything else. For example, if a talented athlete constantly switches teams just to earn more money, never developing loyalty to teammates or fans, someone might describe their approach as mercenary.

Mercenaries differ from volunteers or patriots who fight because they believe in something. While mercenaries might be skilled and effective, their motivation is fundamentally transactional: no payment means no service. This can make them unreliable allies, since they might switch sides if someone offers more money.