After Stalin's death, he was also buried in Lenin's mausoleum. However, after the 20th Congress of the Soviet Union 1956, Khrushchev manipulated a group of Georgians to propose that Stalin's body be moved out of Lenin's mausoleum. Later, Stalin's body was activated and is now buried in Red Square.
It is worth mentioning that there was even a bloody incident in Red Square to defend Stalin's body.