mercenary
This term carries a strong negative connotation when used as an adjective, suggesting a cold, calculating disregard for morality or personal loyalty in favor of financial reward. It implies a transactional nature where principles are traded for profit. As a noun, it refers specifically to soldiers of fortune or individuals driven by greed. While the military sense is descriptive of a professional role, the personal sense is typically a pejorative characterization of someone's motivations.
Meanings
Motivated solely by a desire for monetary gain or profit, often at the expense of ethics or loyalty.
"The politician was criticized for his mercenary approach to diplomacy."
A professional soldier hired to serve in a foreign army.
"The government recruited mercenaries to fight in the border conflict."