Grigory Margulis — math (fields medal) with roots in the USSR
Grigory Margulis is a Russian-American mathematician born in Moscow who received the Fields Medal in 1978 for his groundbreaking work on Lie groups and discrete subgroups. He was unable to travel to receive his medal — the Soviet authorities would not grant him an exit visa. He later emigrated to Yale University.
Tracing the roots — Moscow
Born in Moscow in 1946 and educated at Moscow State University, Margulis is one of the supreme products of the Soviet mathematical tradition. The Soviet authorities' refusal to let him collect his Fields Medal — fearing he would defect — became one of the Cold War's more absurd mathematical episodes. He eventually emigrated and joined Yale.
Moscow. At the time, this region was one of the fifteen republics of the Soviet Union.