Mercenary Ninja

A is a skilled ninja who is hired to fight for another country other than their own in exchange for money.

Before the founding of shinobi villages, the majority of the clans in existence at that point were mercenary military forces for hire by whomever. After shinobi are united in villages, however, such mercenary ninjas fight not out of loyalty to their own country, which would classify them all as missing-nin.

Due to mercenaries not being bound to the laws of the legal shinobi system, it is a risk to employ their services as they may betray their clients, as Zabuza plotted to kill Gatō once he gets enough money, and Hidari and Ashimaru killing Iori amid a mission for a bigger payoff.

Known Mercenaries

 * When Zabuza Momochi, Haku, and the Demon Brothers defected from Kirigakure, they became mercenaries for hire, to acquire funding for a second attempt to assassinate the Mizukage.
 * Kusabi is one of the many mercenaries hired by Gatō to take down the more expensive Zabuza, to save money.
 * Akatsuki is a mercenary group. Their mode of operation is to accept missions at a lower cost than the villages, which in turn will lead the villages to suffer a decline in financial support.
 * Deidara worked as an insurgent terrorist bomber after he defected from Iwagakure and before his forced recruitment into Akatsuki, offering his services to various countries.
 * In the third Naruto movie, the Wandering Ninja Clan is a group of mercenaries of unknown origin hired by Shabadaba.
 * In the anime, the Nokizaru Group is a mercenary ninja team.
 * In the anime, Sadai is the leader of a group of mercenary missing-nin.
 * Kajūra, a terrorist from Ishigakure, used to work for hire, until his arrest by the Counter-Terrorism Division.
 * Etoro Konjiki and Metoro Konjiki, twin brothers from Ishigakure, were in the same terrorist group as Kajūra and specialised in destroying buildings or merchant ships.
 * In the anime, Hidari and Ashimaru began to work as mercenaries when they lost their jobs as regular shinobi after the Fourth Shinobi World War.

Trivia

 * According to Obito Uchiha, back in the days before the hidden villages were created, if one side hired the Senju clan, the other would hire the Uchiha clan, and vice versa, as both were the strongest among all mercenary clans.
 * Despite some mercenary ninja being criminals, they have nevertheless been hired by even the likes of a Kage, as Ōnoki of Iwagakure has hired Akatsuki on many occasions in the past.
 * In Naruto: Shippūden episode 233, a group of mercenary ninja believed Naruto Uzumaki to be a missing-nin and tried to capture him for a bounty they assumed was on his head.