"Grigory Yemelyanovich Klinishov has passed away," the source said.
After graduating from Moscow Engineering Physics Institute in 1954, Klinishov joined a research team at Construction Bureau 11 (KB-11) in what is now Sarov, which was tasked with designing thermonuclear weapons. There he worked as an engineer in the theoretical department under famous Soviet physicist Andrei Sakharov.
The Soviet Union tested its 1.6 megaton thermonuclear bomb, RDS-37, at the Semipalatinsk test site in Kazakhstan in 1955.
After the landmark test, Klinishov went on to design several next-generation thermonuclear weapons. He led the theoretical department at KB-11, which was renamed as the Russian Federal Nuclear Center (under Rosatom), between 1974 and 2001 and was a leading researcher from 2002.