Matvei Bronstein: Theorical physicist. Pioneer of quantum gravity. Arrested, accused of fictional “terroristic” activity and shot in 1938

Lev Shubnikov: Experimental physicist. Accused on false charges. Executed

Adrian Piotrovsky: Russian dramaturge. Accused on false charges of treason. Executed.

Nikolai Bukharin: Leader of the Communist revolution. Member of the Politburo. Falsely accused of treason. Executed.

General Alexander Egorov: Marshal of the Soviet Union. Commander of the Red Army Southern Front. Member of the Central Committee of the Communist Party. Arrested, accused on false charges, executed.

General Mikhail Tukhachevsky Supreme Marshal of the Soviet Union. Nicknamed the Red Napoleon. Arrested, accused on fake charges. Executed.

Grigory Zinoviev: Chairman of the Communist International Movement. Member of the Soviet Politburo. Accused of treason and executed.

Even the secret police themselves were not safe:

Genrikh Yagoda : Right-hand of Joseph Stalin. Head of the NKD Secret Police. He spied on everyone in Russia and jailed thousands of innocents. Yagoda was arrested and executed.

https://en.wikipedia.org/wiki/Genrikh_Yagoda

Nikolai Yezhov : Appointed head of the NKD Secret Police after the death of Yagoda. Arrested on fake charges, executed.

https://en.wikipedia.org/wiki/Nikolai_Yezhov

Everybody was absolutely terrified during this period. At least 600 000 people were killed and over one million people were deported to Gulags in Siberia.