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.

Known Mercenaries

 * When Zabuza Momochi, Haku and the Demon Brothers defected from Kirigakure, they became mercenaries for hire.
 * 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 lower cost than the villages to run cause them 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 Three Wandering Ninja are mercenaries of unknown origin hired by Shabadaba.
 * The Nokizaru Group are a mercenary ninja team.
 * Sadai is the leader of a group of mercenary missing-nin.

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 amongst all mercenary clans.
 * Despite 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 Shippūden episode 233, a group of mercenary ninja believed Naruto Uzumaki to be a missing-nin and tried to capture him for bounty they assumed was on his head.