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.