Semion Yudkovich Mogilevich (June 30th, 1946-) is a Ukrainian-born Russian organized crime boss, believed by European and United States federal law enforcement agencies to be the "boss of bosses" of most Russian Mafia syndicates in the world. He is believed to direct a vast criminal empire and is described by the FBI as "the most dangerous mobster in the world".
Mogilevich's nicknames include "Don Semyon", and "The Brainy Don" (because of his business acumen). He is said to control RosUkrEnergo, a company currently actively involved in Russia–Ukraine gas disputes.
He is based in Moscow, Russia. He has three children and is most closely associated with the Solntsevskaya Bratva crime group. Political figures he has close alliances with include Yury Luzhkov, the former Mayor of Moscow, Dmytro Firtash and Leonid Derkach, former head of the Security Service of Ukraine. Oleksandr Turchynov, former Prime Minister of Ukraine, went to court for allegedly destroying files pertaining to Mogilevich. Mogilevich is believed to have ordered many assassinations of his enemies across the world, including both shootings and car-bombs.