When Lenin died in 1924, Stalin ordered the best doctors and scientists in the Soviet Union to preserve Lenin’s body. It was against Lenin and his wife’s wishes but it was done. Lenin’s mummy was placed in a specially constructed crypt on Red Square. Lenin’s brain was removed to the Soviet Brain Institute, where they determined that the leader’s brain was superior to other human brains–a statement not recanted until 1994. Although some alleged in 1920s, and 1930s that the body on display in the tomb was a wax dummy (because the embalmers had actually failed in their task), the process was thought to be successful–just because before Stalin died, he asked his body to be preserved and placed in the crypt alongside Lenin.
[In the 30s, the Soviet government opened an official “investigation” into the matter and invited a German doctor to participate and report his findings to the world. However, the doctor was allowed only a cursory examination, and was prohibited from inquired about the secret embalming formula. The doctor nonetheless observed frostbites on the skin, felt the cheeks, and lifted one of Lenin’s arms.]
Later during a period of de-Stalinization undertaken by Krushchev, Stalin’s body was removed under cover of night and buried in a modest tomb alongside the Kremlin wall. Krushchev ordered thick layers of concrete to be placed over the tomb so that Stalin could never rise again.
The above picture is through Pictorial Parade. For more information about the mausoleum, [link]