Sergei Mironovich Kostrikov or better known as Sergei Kirov (born 27 March 1886, O.S. 15 March, Urzhum, Russian Empire – died 1 December 1934, Leningrad, RSFSR, Soviet Union), was a Soviet politician and Bolshevik revolutionary whose assassination led to the first Great Purge in 1936, that was organised by Joseph Stalin and the NKVD (Genrikh Yagoda, Nikolai Yezhov and Lavrenty Beria).

Sergei Kirov joined the RSDLP in 1904 led by Lenin. Sergei Kirov was involved in the 1905 Russian Revolution until it ended in 1907. He then moved to the Caucasus where he stayed until the [1917 Russian Revolution and Tsar Nicholas II was forced to abdicate the throne ending the long Russian Monarchy. He was also involved in the Russian Civil War of 1917 until it ended in 1923. Sergei Kirov was also involved in the 1918-1921 Polish–Soviet War until it ended in 1921 just two years before both Russian Revolution and the Russian Civil War ended in 1923 in the Soviet Union. Lenin died in 1924 aged 54 and Felix Dzerzhinsky, Alexei Rykov, Leon Trotsky and Lev Kamenev, all tried to replace Lenin, but it was Joseph Stalin who came to power in 1924. Stalin and Kirov were friends until Kirov was shot and killed in 1934 at the age of 48, possibly by the NKVD on the order of Stalin. And it led Stalin to kill Alexei Rykov, Lev Kamenev and other Leninists. Stalin had Genrikh Yagoda and Nikolai Yezhov executed in 1938 and 1940 by Lavrentiy Beria. Stalin ordered Leon Trotsky to be assassinated in August 1940 during the Second World War, who had fled to Mexico in 1937.

He was the First Secretary of the Communist Party of Azerbaijan and the leader of the Azerbaijan SSR, between 1921 and 1926.

He was Chief of the Communist Party of the Soviet Union in Leningrad, from 1927 until he was assassinated on 1 December 1934.

The city Kirov and Kirov Oblast are named after Sergei Kirov.

It is speculated by historians, that the Soviet leader Joseph Stalin ordered his assassination, because he saw Kirov, who was popular, as a threat to his rule, and started the Great Purge as an excuse to eliminate all his real and potential rivals.