Mercenary
MERCENARY (Lat. mercenarius, from merces, reward, gain), one who serves or acts solely for motives of personal gain, particularly a soldier who offers himself for service in any army which may hire him. The name is sometimes used as a term of reproach by nations who raise their armies by conscription, of armies raised by voluntary enlistment whose members are paid a more or less living wage.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)