Resigned and the soviet union ceased to exist on christmas day in 1991.

josef stalin

boris yeltsin

leonid brezhnev

mikhail gorbachev

Mikhail Gorbachev

Explanation:

The resignation took place on the Christmas of 1991, as Mikhail Gorbachev announced the decision to cease as head of state and to dismember the Soviet Union, declaring a consitution of the Russian Federation.

The other USSR member states already had begun to form separate republics and a Commonwealth . The CIS stands for the countries resulting from this.

The constitution of a Russian Federation was meant to incorporate the urgent changes in the economy, the politics ,  and the modernization of infrastructures across the country. Gorbachev opened doors to colaboration with the west. that ended the Cold war politics- Furthermore he sought a market economy based on the principles of liberalism.

Among other changes were the reduction in the nuclear war  heads from the arms race.