Answer
Serving as the Mayor of Petrograd, Mikhail Kalinin played a significant role during the October Revolution of 1917. He was actively involved in the Bolshevik Party's efforts to overthrow the Provisional Government and establish Soviet power. As the head of the Petrograd Soviet, Kalinin coordinated with other revolutionary leaders such as Lenin and Trotsky to organize the Red Guards and mobilize workers and soldiers in support of the Bolshevik cause.