Semion Mogilevich

Semion Yudkovich Mogilevich (Russian: Семён Юдкович Могилевич, IPA: [sʲɪˈmʲɵn ˈjutkəvʲɪtɕ məɡʲɪˈlʲevʲɪtɕ]; Ukrainian: Семен Юдкович Могилевич, romanized: Semén Yúdkovych Mohylévych, IPA: [seˈmɛn ˈjudkowɪtʃ moɦɪˈlɛwɪtʃ]; born June 30, 1946) is a Ukrainian-born Russian organized crime boss. He is described by agencies in the European Union and United States as the "boss of all bosses" of most Russian Mafia syndicates in the world, he is believed to direct a multi billion-dollar international criminal empire and is described by the Federal Bureau of Investigation (FBI) as "the most powerful and dangerous gangster in the world," with immense power and reach at a global scale, and connections to prominent government, military, and law enforcement officials, and powerful politicians around the world. He has been accused by the FBI of "weapons trafficking, contract murders, extortion, drug trafficking, and prostitution on an international scale."

Mogilevich's nicknames include "Don Semyon" and "The Brainy Don" (because of his business acumen). According to US diplomatic cables, he controls RosUkrEnergo, a company actively involved in Russia–Ukraine gas disputes, and is a partner of Ivan Gordiyenko.

Oleksandr Turchynov, who was designated the acting President of Ukraine in February 2014, appeared in court in 2010 for allegedly destroying files pertaining to Mogilevich. Shortly before his assassination, Russian FSB defector Alexander Litvinenko claimed Mogilevich had a "good relationship" with Vladimir Putin from the 1990s.

William S. Sessions, Director of the FBI from 1987 to 1993 during the presidencies of Ronald Reagan and George H. W. Bush, was Mogilevich's attorney in the United States until Sessions' death on June 12, 2020.