Answer:
The leader that was a member of the Communist Party, but made the most changes against Communism when he took office was Mikhail Gorbachev.
Step-by-step explanation:
Mikhail Gorbachev is a Russian politician who served as the last secretary-general of the Soviet Communist Party from 1988 to 1991.
His attempts at reform led to a diminution and an end to the Cold War, for which he was awarded the Nobel Peace Prize, but at the same time the Soviet Communist Party lost its former political power, eventually leading to the dissolution of the Soviet Union.