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.
To be fair, having authoritarian government means you’ll absolutely have an oppressive regime at some point.
If anything, Stalin was the one to cement authoritarianism as the system of power in USSR and make sure it cannot be reverted without massive issues in the form of separatism, civil disobedience, and more. The subsequent leaders could only open the valve of democracy so much without breaking the country apart.
So, it’s not just leaders, it’s the system of authoritarian power and imperialism. Communism and socialism must be democratic and directly managed by worker’s councils, bottom to top (i.e. Soviet in its original sense), lest you fall into the same trap with any leader eventually.