According to this article, Stalin wanted to created super-soldiers by cross breeding humans with apes:

"Moscow archives show that in the mid-1920s Russia's top animal breeding scientist, Ilya Ivanov, was ordered to turn his skills from horse and animal work to the quest for a super-warrior. According to Moscow newspapers, Stalin told the scientist: "I want a new invincible human being, insensitive to pain, resistant and indifferent about the quality of food they eat."

(via)