Nikolai Ivanovich Yezhov or Ezhov (Russian: Никола́й Иванович Ежо́в) (IPA: [nʲɪkɐˈlaj jɪˈʐof]; May 1, 1895 – February 4, 1940) was the senior figure in the NKVD (the Soviet secret police) under Joseph Stalin during the period of the Great Purge. His reign is sometimes known as the "Yezhovshchina" (Russian: Ежовщина), "the Yezhov era", a term that began to be used during the de-Stalinization campaign of the 1950s. During the beginning of World War II his status within the USSR became that of a political unperson.

Yezhov was born in Saint Petersburg, according to his official Soviet biography, though other records^[specify] point to the possibility that he was born in Marijampolė. In a form filled out in 1921, Yezhov claimed some ability to speak Polish and Lithuanian.

He completed only his elementary education. From 1909 to 1915, he worked as a tailor's assistant and factory worker. From 1915 until 1917, Yezhov served in the Imperial Russian Army. He joined the Bolsheviks on May 5, 1917 in Vitebsk, seven months before the October Revolution. During the Russian Civil War, 1919–1921, he fought in the Red Army. After February 1922, he worked in the political system, mostly as a secretary of various regional committees of the Communist Party. In 1927, he was transferred to the Accounting and Distribution Department of the Communist Party where he worked as an instructor and acting head of the department. From 1929 to 1930, he was the Deputy People's Commissar for Agriculture. In November 1930, he was appointed to the Head of several departments of the Communist Party: department of special affairs, department of personnel and department of industry. In 1934, he was elected to the Central Committee of the Communist Party; in the next year he became a secretary of the Central Committee. From February 1935 to March 1939, he was also the Chairman of the Central Commission for Party Control.