Sergei Kostrikov took part in the 1905 revolution, was arrested and released in about three months. He joined the bolsheviks soon after being released from prison. In 1906 Kostrikov was arrested once again, but this time for over three years, charged of printing illegal literature. Soon after his release, he took part in revolutionary activity. Once again being arrested for printing illegal literature, after a year of custody, Kostrikov moved to the Caucasus where he stayed until the abdiction of Nicholas II.
By this time Sergei Kostrikov had changed his name to Kirov. He had selected it as a pen name, just as other Russian revolutionary leaders. The name "Kir" reminded him of a Persian warrior king, and he was to become head of the Bolshevik military administration in Astrakhan.
Following the 1917 Russian Revolution he fought in the Russian Civil War until 1920. In 1921 he became head of the Azerbaijan party organisation. Kirov loyally supported Joseph Stalin, and in 1926 he was rewarded with the leadership of the Leningrad party.
In the 1930s, Stalin became increasingly worried about Kirov's growing popularity. In 1934, Stalin asked Kirov to work for him in Moscow, most probably to keep a closer eye on him. Kirov refused, however, and in Stalin's eyes became a competitor.
On December 1, 1934, Kirov was assassinated by Leonid Nikolaev, a young party member. Stalin claimed that Nikolayev was part of a larger conspiracy led by Leon Trotsky against the Soviet government. This resulted in the arrest and execution of Genrikh Yagoda, Lev Kamenev, Grigory Zinoviev, and fourteen others in 1936. It is widely believed that Stalin was the man who ordered the murder of Kirov, but this has never been proven.