Sergei Stanislavovich Udaltsov (Russian: ?????ยด? ????????????? ????????; born 16 February 1977) is a Russian political activist.
He is the unofficial leader of the Vanguard of Red Youth (AKM).
In 2011 and 2012, he helped lead a series of protests against Vladimir Putin.
In 2014 he has been sentenced to 4 1/2 years in a penal camp for organizing the May 2012 protest which ended in violence between the police and demonstrators.