Abu Omar Al-Baghdadi (an alias) first came to notice on October 12, 2006 and has been not just the replacement for Zarqawi but a figure on par with the Taliban's Mullah Omar or some may say Osama Bin Laden. This time it appears the U.S. military and the media does not want to give him the same notoriety. Khalid al-Mashhadani is the best guess on the Abu Omar's real identity
The Islamic State of Iraq was formerly known as al qaeda between the two rivers and before that Monotheism and Jihad. Zarqawi said that he swore allegiance to Osama bin Laden and his al qaeda organization creating a link that did not exist before the war. The name "al qaeda" has no historical or political history in Iraq but has been used frequently by the U.S. to describe foreign volunteers who fight in other regions. Zarqawi was just another foreigner who had appeared in a foreign country to fight jihad. But his tactics and violence were condemned by Dr Ayman Zawahiri and terrified Iraqis who did not share his need for bloodletting.
On January 15, 2006, Al Qaeda Between the Two Rivers created the Shura Council of the Mujaheddin creating a Iraqi leader (Zarqawi was Jordanian, not Iraqi) Abdullah Rashid al-Baghdadi of the Quraish tribe (not Abu Omar..the term "al Baghdadi" is a place of origin), Zarqawi was killed in an airstrike on June 7, and Abu Hamza al-Muhajir took over the operational control.
On October 12, 2006, Al Qaeda Between the Two Rivers created a larger organization of Sunni groups by creating a Shura called the Islamic State of Iraq led by "Abu Omar al-Baghdadi" who was voted as "Emir" of this self-declared state. In November Abu Hamza al-Muhajir pledged allegiance to the "Islamic State of Iraq". Two important things occured. first, Abu Omar al-Baghdadi is the titular leader of the Sunni insurgency in Iraq and "al qaeda" has taken a back seat to nationalistic and religious forces. Currently Diyala province is the white hot focus on the Salfist leader and their violent efforts. with the Mahdi Army being the natural counterpoint to the Sunni movement, the U.S. may find itself in the middle of two well organized, determined groups intent on creating transnational powerbases.
Scholar Nibras Kazimi has the original text and excellent insights on the evolution on structure of the Sunni movement to establish a Caliphate. You can read the December 2006 speech here and the February speech here
Al qaeda began as one of the many nick names of the arabic-speaking volunteers who came to Afghanistan to fight the Soviets. Osama bin Laden emerged as the heir apparent of Abdullah Azzam and since 9/11 has been the enigmatic target of the Global War on Terror. With the emergence of Al Baghdadi and his restructuring of the jihad in Iraq as a global focal point for struggle against apostates, Zionists and crusaders he is stepping into the shoes of al qaeda and bin laden and with a much more violent impact.
I have often pointed out the function of franchising in terrorism. A situation in which foreign non-state players provide a template under the al qaeda brand. Complete with proxy leaderships and manifestos.
Veterans gather together local volunteers who then communicate their expertise, training, funding and ideological skills to lay the direction of an insurgent movement. Once the locals have been trained and learned how to fund themselves they can then gather momentum towards nationalistic and political directions. It is clear that the franchise of al qaeda is being replaced by a robust internal movement with its own tactics and resources. It is similar model used by U.S. Army Special Forces to train and support insurgent groups and it has been refined and expanded by our enemies to great effect. Our methods have lagged with the enemy rapidly adopting both high tech (internet and MPEGS) and ancient resources (halwallahs and messengers) to great effect.
The evolution of the Salafist and Shia movements in Iraq are evidence that we are well behind the curve in the Global War on Terror.