Leonid Fedorovych Toptunov (Ukrainian: Леонід Федорович Топтунов, Russian: Леонид Фёдорович Топтунов; 16 August 1960 – 14 May 1986) was a Soviet electrical engineer who was the senior reactor control chief engineer at the Chernobyl Nuclear Power Plant Reactor Unit 4 on the night of the Chernobyl disaster, 26 April 1986.

[1] Leonid Toptunov was born on 16 August 1960 in Mykolaivka, Buryn Raion, Sumy Oblast, Ukraine.

During his studies of the reactor documentation, he mentioned to his friend, Sasha Korol, that control rods may, in certain circumstances, accelerate rather than slow the reaction.

[3] The operators attempted to perform a rundown test before scheduled routine maintenance, during which reactor 4 exploded.

Withdrawing a dangerous number of control rods, the operators could only reach 200 MW due to xenon poisoning.

[3] Due to a design flaw, the descending control rods momentarily accelerated the nuclear reaction and caused the reactor to explode.

[5] In 2008, Toptunov was posthumously awarded with the 3rd degree Order For Courage by Viktor Yushchenko, then the President of Ukraine.