Who was the ussr leader who reversed the cold war with a policy called which means openness?

Gorbachev--Began the glasnost campaign to open the USSR up both socially and politically. 

Mikhail Gorbachev started the glasnost program with the goal of reforming the USSR. It included talks with the US and Reagan about ending the arms race as well as limiting weapons. It also began to democratize the USSR with open elections and freedom to criticize the government.