The Rapid Support Forces (RSF) have been accused of widespread abuses in Sudan, including the 3 June massacre in which more than 120 people were reportedly killed, with many of the dead dumped in the River Nile. Sudan expert Alex de Waal charts their rise.

The RSF are now the real ruling power in Sudan. They are a new kind of regime: a hybrid of ethnic militia and business enterprise, a transnational mercenary force that has captured a state.

Their commander is General Mohamed Hamdan "Hemeti" Dagolo, and he and his fighters have come a long way since their early days as a rag-tag Arab militia widely denigrated as the "Janjaweed".

The RSF was formally established by decree of then-President Omar al-Bashir in 2013. But their core of 5,000 militiamen had been armed and active long before then.

Their story begins in 2003, when Mr Bashir's government mobilised Arab herders to fight against black African insurgents in Darfur.

'Meet the Janjaweed'

The core of the Janjaweed were camel-herding nomads from the Mahamid and Mahariya branches of the Rizeigat ethnic group of northern Darfur and adjoining areas of Chad - they ranged across the desert edge long before the border was drawn.

During the 2003-2005 Darfur war and massacres, the most infamous Janjaweed leader was Musa Hilal, chief of the Mahamid.

As these fighters proved their bloody efficacy, Mr Bashir formalised them into a paramilitary force called the Border Intelligence Units.

One brigade, active in southern Darfur, included a particularly dynamic young fighter, Mohamed Dagolo, known as "Hemeti" because of his baby-faced looks - Hemeti being a mother's endearing term for "Little Mohamed".

A school dropout turned small-time trader, he was a member of the Mahariya clan of the Rizeigat. Some say that his grandfather was a junior chief when they resided in Chad.

A crucial interlude in Hemeti's career occurred in 2007, when his troops became discontented over the government's failure to pay them.

They felt they had been exploited - sent to the frontline, blamed for atrocities, and then abandoned.

Hemeti and his fighters mutinied, promising to fight Khartoum "until judgement day", and tried to cut a deal with the Darfur rebels.

A documentary shot during this time, called Meet the Janjaweed, shows him recruiting volunteers from Darfur's black African Fur ethnic group into his army, to fight alongside his Arabs, their former enemies.

Although Hemeti's commanders are all from his own Mahariya clan, he has been ready to enlist men of all ethnic groups. On one recent occasion the RSF absorbed a breakaway faction of the rebel Sudan Liberation Army (SLA) - led by Mohamedein Ismail "Orgajor", an ethnic Zaghawa - another Darfur community which had been linked to the rebels.

Consolidating power

Hemeti went back to Khartoum when he was offered a sweet deal: back pay for his troops, ranks for his officers (he became a brigadier general - to the chagrin of army officers who had gone to staff college and climbed the ranks), and a handsome cash payment.

His troops were put under the command of the National Intelligence and Security Service (NISS), at that time organising a proxy war with Chad.

Some of Hemeti's fighters, serving under the banner of the Chadian opposition, fought their way as far as the Chadian capital, N'Djamena, in 2008.

Meanwhile, Hemeti fell out with his former master, Hilal - their feud was to be a feature of Darfur for 10 years. Hilal was a serial mutineer, and Mr Bashir's generals found Hemeti more dependable.

In 2013, a new paramilitary force was formed under Hemeti and called the RSF.

The army chief of staff did not like it - he wanted the money to go to strengthening the regular forces - and Mr Bashir was worried about putting too much power in the hands of NISS, having just fired its director for allegedly conspiring against him.

So the RSF was made answerable to Mr Bashir himself - the president gave Hemeti the nickname "Himayti", meaning "My Protector".

Training camps were set up near the capital, Khartoum. Hundreds of Land Cruiser pick-up trucks were imported and fitted out with machine guns.

RSF troops fought against rebels in South Kordofan - they were undisciplined and did not do well - and against rebels in Darfur, where they did better.

Gold rush

Hemeti's rivalry with Hilal intensified when gold was discovered at Jebel Amir in North Darfur state in 2012.

Coming at just the moment when Sudan was facing an economic crisis because South Sudan had broken away, taking with it 75% of the country's oil, this seemed like a godsend.