The Allied Democratic Forces (ADF), a Ugandan-led Islamist armed group that has been active in North Kivu's Beni territory since 1996, is one of the oldest in eastern DRC, but it is also one of the most mysterious.
Ugandan rebel leader Jamil Mukulu set up this coalition of groups in western Uganda after they found themselves marginalised following the fall of the dictator Idi Amin. The insurgency is reported to be supported by the Government of Sudan, which also fought the Government of Uganda.
'Deaths by crucifixion'
The ADF, with an estimated 1,200 to 1,500 armed fighters, launched a series of attacks in 2013 against civilians in the DRC, forcing thousands of people to flee into Uganda and abducting or killing those that attempted to return.
The ADF was also responsible for brutal attacks on women and children in several villages, including acts of beheading, mutilation, and rape.
According to Human Rights Watch, "civilians who had earlier been held in ADF camps said they saw deaths by crucifixion, executions of those trying to escape, and people with mouths sewn shut for allegedly lying to their captors".
Some captives accused of "misbehaving" were held in holes or in a caskets lined with nails for days or more than a week. The attackers also raped women and forced them to be their "wives."
Check out our Flipboard magazine - Who's who in the battle for DRC by IBTimes UK
In this series on the Democratic Republic of the Congo, IBTimes UK takes a closer look at the eastern regions of South and North Kivu where civilians are still at the mercy of armed groups and the Congolese armed forces, who have all been accused of committing serious war crimes.