Lost Cosmonauts, or Phantom Cosmonauts, is a conspiracy theory alleging that cosmonauts entered outer space, but without their existence having been acknowledged by either the Soviet or Russian space authorities.
Proponents of the Lost Cosmonauts theory concede that Yuri Gagarin was the first man to survive space travel, but claim that the Soviet Union attempted to launch two or more manned space flights prior to Gagarin's, and that at least two cosmonauts died in the attempts. Another cosmonaut, Vladimir Ilyushin, is believed to have landed off-course and been held by the Chinese government. The Government of the Soviet Union supposedly suppressed this information, to prevent bad publicity during the height of the Cold War.