Valery Legasov (played by Jared Harris) was the first deputy director of the Kurchatov Institute of Atomic Energy at the time of the Chernobyl crisis. The scientist investigated the cause of the disaster and planned the mitigation of its consequences. According to The Los Angeles Times, his foreign colleagues praised his honesty in talking about the cause and effects of the accident. He attributed the disaster to design flaw and human error.
Legasov committed suicide in 1988, reportedly leaving behind tapes with undisclosed information about Chernobyl. He implied that political pressure censored bringing up the Soviet nuclear secrecy that kept plant workers in the dark about known problems and accidents with the reactor model.