There are rebels in the fractious nation of Congo who call themselves "Ninjas." Apparently they formed an opposition party sometime around 2002. From the BBC timeline:
2002 March - Intense fighting between government and "Ninja" rebels drives many thousands of civilians from their homes in Pool region. The rebels, loyal to former PM Bernard Kolelas and led by renegade priest Pastor Ntumi, name themselves after the famous Japanese warriors.
2002 June - Government troops battle Ninja rebels in Brazzaville. About 100 people are killed.
2003 March - Government signs deals with Ninja rebels aimed at ending fighting in Pool region. Ninja leader Pastor Ntumi agrees to end hostilities and allow the return of the rule of law.
2004 June - World diamond trade watchdog removes Congo from list of countries recognised as dealing legitimately in diamonds.
2005 April - Government says a group of army officers, arrested in January over an arms theft, had been planning a coup.
2005 October - Former PM Bernard Kolelas is allowed home to bury his wife after eight years in exile, during which time he was sentenced to death on war crimes charges. He is given an amnesty in November.
2006 January - Congo is chosen to lead the African Union in 2006 after disagreements within the body about Sudan's leadership bid.
President Sassou-Nguesso accuses France of interfering in his country's affairs, following a decision by a French Appeal court to reopen an investigation into the disappearance of more than 350 refugees in 1999.
2007 June - Former "Ninja" rebels led by renegade Pastor Frederic Ntoumi ceremoniously burn their weapons to demonstrate their commitment to peace.
But don't be so sure these "ninjas" have actually laid down their arms. While they are certainly not real ninjas, their very name would seem to suggest a willingness to attain their ends by any means necessary, including but not limited to deception and stealth. The "peaceful ninjas" of June 2007 have now arrived in September looking less-than-peaceful. From Reuters:
A renegade pastor due to take up a ministerial position in Congo Republic was prevented from entering the capital Brazzaville on Monday when he arrived with 3,000 armed men, a government spokesman said.
Frederic Bintsamou, better known as Pastor Ntoumi, fought a rebellion in the Pool region around Brazzaville from 1998 to 2003, when he signed a peace agreement with President Denis Sassou-Nguesso...
"He arrived with more than 3,000 armed ex-combatants, while he is permitted a guard of 30 people," said government spokesman Alain Akouala, adding that some of the former fighters carried machine guns and rocket launchers, and harassed civilians.
"The principle of his taking office remains in place, but we do not want to name a day," Akouala said. "Frederic Bintamou can rest assured that his safety will be guaranteed."
Ntoumi's "Ninja" rebel movement, named after the Japanese warriors, became a political party following the peace deal, the National Council of Republicans (CNR), but failed to win a single seat at legislative elections in June.
Army general Sassou-Nguesso took office at the head of military regime in 1979 and ruled for 13 years before losing elections in 1992. He returned to power in an Angolan-backed uprising in 1997 which sparked a two-year civil war.