It's surmised by many that what happened in Mosul was a "coup" led by Izzat Ibrahim al-Douri; with other groups led by former Baath officers, Al-Douri has been playing an active role in various Sunni majority areas of Iraq .... that he was one of the senior commanders at the helm for the successful take over of Mosul via the rebel groups.
If you aren't sure who Al-Douri is .. during Saddam Hussein's era he used to be one of Saddam's most trusted military commanders. He was one of the very few Baathists who evaded capture. Al-Douri was made the new leader of the banned Baath Party soon after Saddam's execution in 2006.
According to a story that began in 2003, Izzat Ibrahim Al-Douri who is now aged 70 has been suffering from leukemia since 1999 or earlier and requires to undergo blood transfusion every six months. If this was true, Al-Douri should have been dead long ago. There is no way he could have survived with such a serious health issue nor received regular blood transfusions soon after Iraq fell in 2003 when he was a wanted man and in hiding. Also, a 70-year-old suffering from leukemia for more than 16 years would be in no condition to actively participate in a coup as reported on Al-Douri.
Al-Akhbar suggests Izzat Al-Douri has been silently working on a coup since long. Over time he was able to establish a network of former Baath officers who were kicked out of the military by Iraq's Shiia government. Al-Douri used ISIS as a facade to frighten and terrorize his opponents. But in reality it was probably the other way round. Knowing Al-Dour's longstanding popularity in Sunni circles, it might be ISIS that's using his name to cajole the residents of Mosul. This is one possibility. The other one is that the Naqshbandi militias are using Al-Douri's image to acquire support of the people of Mosul. Naqshbandi group is a Sufi resistance movement and Izzat al-Douri is supposed to be one of it's many senior associates.
However, a former member of the Baath Party residing in Mosul confirmed to Niqash media outlet that Al-Douri has not been living nor seen in Mosul for years. That tallies with some other contents of the story via Niqash on June 13. It reported that a day after the fall of Mosul, gunmen with automatic weapons went around telling the people of the city to gather at "central square" where Al-Douri would be giving a speech to celebrate the event. Hundreds of excited residents went to central square with their cameras and mobile phones. But the person who emerged to give the speech was not Al-Douri. He was some other old and bearded man, never seen nor heard of before. He never even mentioned the name of Al-Douri. The crowd was very disappointed. Later it was again announced on Facebook and Twitter that Al-Douri would be giving a televised speech. That turned out to be an old speech which Al-Douri had given on Al-Arabiya more than a year ago. The tricks are obvious. Either the Naqshbandis or ISIS (most likely the Naqshbandis) are using Al-Douri to keep the residents of Mosul calm and happy in their day dreams.
By the way, ISIS and the Naqshbandi army are not on the best of terms. The former has often furiously objected to the posters of Saddam Hussein put up by the latter.
ISIS is likely using the Naqshbandi Army and their links to the Baath party for its own benefit. But while the Naqshbandi movement can cooperate with the Baathists, neither of the two would be able to manage an alliance with ISIS which is too demanding, selfish and unprincipled to respect a partnership or a coalition for longer than a few weeks.
Smaller groups like Ansar al-Sunna and Mujahideen Army are also purportedly appearing in Mosul. Niqash writes that the people of Nineveh province have been seen welcoming the different factions of militants. Undoubtedly, there is a huge sectarian element in this entire scenario. Nouri al-Malki's fiercely sectarian policies, blatant discrimination against Iraqi Sunnis along with his government's daily injustices and mind boggling corruption pushed the Sunni population of Nineveh province over the edge and consequently they chose the Sunni militants over Al-Malki as the better of the two evils.