About Valentin Bondarenko
Valentin Vasilyevich Bondarenko was a Soviet fighter pilot selected in 1960 for training as a cosmonaut. He died as the result of burns sustained in a fire during a 15-day low-pressure endurance experiment in Moscow. The Soviet government concealed the death, along with Bondarenko's membership in the cosmonaut corps, until 1980. A crater on the Moon's far side is named after him. Bondarenko, "(also known as 'Valentin Junior' and 'Tinkerbell') was the youngest member of the cosmonaut team." He began training on 31 May for a planned launch on the crewed Vostok spacecraft. On 28 April 1960, Bondarenko was chosen to be among the first group of 20 cosmonauts. Bondarenko died of shock 16 hours after the accident, less than three weeks before Gagarin's first spaceflight aboard Vostok 1.
Biography source: Wikipedia. The profile adds birthday-specific historical context from the Celebs Birthday Today editorial database.