WHO IS DOKU UMAROV”?

◼ The Chechen Bin Ladenl terrorist's profile rises amid Boston bombing speculation - FOX

Doku Umarov could be one of the most important — and dangerous — terrorists Americans have never heard of.

The Chechen Islamic radical, who leads a group called the Caucasus Emirate, for years has been one of Russia’s most-wanted men. He and his organization have claimed responsibility for attacks killing dozens of civilians, including the 2010 Moscow subway bombings. Since 2011, the U.S. State Department has offered $5 million for information on his whereabouts.

Though nicknamed Russia’s bin Laden, his name never had the global resonance of Al Qaeda’s founder or its deputies. But in the wake of the Boston Marathon attack, Umarov is receiving worldwide attention.

Whether he or the Caucasus Emirate are in any way connected to the bombing is not known. Sources told Fox News that investigators are looking into possible ties between Tamerlan Tsarnaev, the suspect who died in a shootout early Friday in Boston, and the Caucasus Emirate.

A U.S. official said Tuesday that the “working theory” is they were motivated by radical Islam but acted alone. Still, officials have not determined what the older brother was doing during a mysterious six-month trip to Russia last year.

Though Umarov is not as well known in the U.S. as some other wanted terrorists, he is in the top tier. The 2011 world’s most-wanted list, put out by Forbes, listed him along with the likes of Al Qaeda chief Ayman al-Zawahiri and brutal Ugandan warlord Joseph Kony....

According to a 2011 report by the Center for Strategic and International Studies, Umarov has since 2007 declared “jihad against anyone fighting against Muslims anywhere across the globe.”

The Caucasus Emirate, the extremist group he leads, was formed in 2007. It grew out of the flagging separatist group the Republic of Ichkeria, which Umarov helped lead in various positions since the first Russian-Chechen war. He climbed the ladder until creating the Caucasus Emirate and declaring himself emir.

Umarov was already wanted in Russia — the country charged him with murder in 1992, and an international arrest warrant was issued in 2000 — before the formation of the CE, but his group’s crimes have since attracted more global attention.

He claimed responsibility for the 2010 Moscow bombing of two subway stations, which killed 40, and the 2011 attack on a Moscow airport which killed nearly as many.

◼ FLASHBACK, 2007: ‘CHECHEN OSAMA BIN LADEN’ DECLARES WAR ON AMERICA - Pat Dollard

◼ Chechnya: In Video, Separatist Leader Declares 'Jihad' On West - Radio Free Europe/Radio Liberty

For more on the Chechen separatist movement, see RFE/RL's analysis, ◼ Is North Caucasus Resistance Still Serious Threat?