Comintern

The Comintern, also known as the Third International or the Communist International, existed from 1919 to 1943. The Comintern was the center for helping Communist activities worldwide; it was in Moscow only because Russia was the first nation to come under Communist control. In Marxist-Leninist theory, it was inevitable that other nations would become Communist, so the Comintern looked at those national Communist parties as simply being local offices of the International. The extent to which national parties followed this varied by country, but, in the beginning, support was often enthusiastic for the one successful revolution.

In the Bolshevik Revolution of 1919, headed by Vladimir Lenin, there were factions  focused on the world-revolution model of  Leon Trotsky, as opposed to the control-Russia-first model of Josef Stalin. With Stalin's establishing control, the need for the Comintern diminished, and simply was not important to him in the middle of the Second World War.

Leadership
The first president of the Comintern, who served from 1919 to 1926, was Grigory Zinoviev, of the "left" faction, headed the Comintern from 1919 to 1926. He was not popular in the party, and eventually purged by Stalin. The position was then formally abolished, but actual control passed to Nikolai Bukharin, of the "right" faction, who lasted until 1928.

There was no clear leader until 1935, until Georgi Dimitrov, a Bulgarian Communist, became secretary general of the Comintern's Executive Committee.