Stalin's cult of personality

Joseph Stalin's cult of personality became a prominent part of Soviet culture in December 1929, after a lavish celebration for Stalin's 50th birthday.[1] For the rest of Stalin's rule, the Soviet press presented Stalin as an all-powerful, all-knowing leader, and Stalin's name and image became omnipresent. From 1936 the Soviet journalism started to refer to Joseph Stalin as the Father of Nations.

End of the cult and de-Stalinization
In his 1956 ""Secret Speech" " to the Twentieth Party Congress, Nikita Khrushchev famously denounced Stalin's cult of personality, saying, "It is impermissible and foreign to the spirit of Marxism-Leninism to elevate one person, to transform him into a superman possessing supernatural characteristics akin to those of a god." The "Secret Speech" initiated a political reform, known as De-Stalinization, that sought to eradicate Stalin's influence on the Soviet society.

More information on the Wikipedia page.