His 108-minute flight into space 50 years ago set new a horizon for humanity and overnight turned a farmworker's son named Yuri Gagarin into one of the century's heroes.
But half a century after his exploit captured the world's imagination and fueled a space race with the United States, Russia has found it necessary to release top secret archives to counter persistent rumors that Gagarin was later murdered on the orders of jealous or paranoid Soviet leaders.
"Gagarin once said: "˜To me my whole life seems to be one perfect moment,'" recalled veteran Soviet space journalist Vladimir Gubarev earlier this month.
The 27-year-old's single Earth orbit on April 12, 1961 was one of the Soviet Union's most enduring Cold War victories and is proudly remembered today, especially in the cosmonaut town that is the heart of the nation's space program.
Star City, the world's oldest space-flight training center, resembles in many ways a shrine to the first man in space, whose premature death in a mysterious plane crash seven years after his flight cemented a poster-boy status.
Visitors on a rare open day were greeted by a lone statue of Gagarin dominating the snowy paths between worn buildings scattered behind a perimeter fence in a pine forest outside Moscow like some isolated university campus.
A mural of the national hero leads into a small museum hall filled with memorabilia: Gagarin's orange-brown space suit, gifts from foreign dignitaries and a room that painstakingly re-creates his office as it was on the day he died.
One striking photo shows Gagarin's round orbiter, scorched from its fiery descent, lying in a field in Russia's central Saratov region, where he was famously offered milk and bread by an astonished farmworker moments after landing.
New evidence on death
Conspiracy theories abound that he did not die in a plane crash, but was murdered on the orders of Soviet leader Leonid Brezhnev for an unspecified offence or disloyalty to the party.
In an apparent bid to quash such whisperings about Gagarin's death ahead of the anniversary, the archives declassified by post-Soviet Russia last week shed new light on the crash.
The documents show a Soviet probe concluded that Gagarin had most likely lost control of his jet after swerving sharply to avoid a weather-forecasting balloon, archives official Alexander Stepanov was quoted by Russian news agencies as saying.
Gagarin's maiden orbit nearly ended in disaster. "For 10 whole minutes of his flight, he thought he was dead," said Gubarev, who knew Gagarin as a young fighter pilot.
"The flight was absolutely heroic. It was unimaginably difficult. People thought a man might go crazy in space," he told Reuters.
When Gagarin's Vostok-1 capsule hit the atmosphere on re-entry, the cables hooking the descent module to the service module failed to separate.
The craft shook violently before they burned loose and Gagarin was sucked down by gravity. He experienced G-forces -- the force of gravity on a body -- two to three times steeper than those felt by today's astronauts.
"When I dream now, it is mostly nightmares about the descent," said veteran cosmonaut Georgy Grechko, 79, who worked as an engineer on Gagarin's space capsule.
"When the craft re-enters the thick levels of the Earth's atmosphere, it burns. The flames tear at the craft. It rolls and the coating melts. It's scary."
A letter Gagarin drafted to be sent to his family in case he died was among the documents declassified last week, and offered a glimpse into the steely-eyed courage of the young pilot.
"I trust the hardware completely. It will not fail. But it can happen that a man trips at ground level and breaks his neck. Some accident may happen," the letter previewed by opposition paper Novaya Gazeta said.
"If it does... do not waste yourself with grief. Life is life, and nobody is safe from being run over by a car."
From farm boy to space icon
The Soviet Vostok-1 spaceship lies at the landing site 700 km south-east of Moscow after the first manned space trip in 1961.
The 19 candidates selected for the Vostok-1 flight were all test pilots, unafraid of speed, and slight enough in build to fit into the tiny 2m-wide (6ft) capsule.
The Soviet-era charm of Gagarin's humble roots may have favored him over others, including his backup Gherman Titov.
Born in the village of Klushino, some 150 km (95 miles) west of Moscow, his father was a carpenter and his mother a milkmaid. The family was forced to live in a tiny mud hut when the village was burned down during the German occupation in World War Two.
"Yura (Gagarin) was a very quick learner. He assimilated everything new. His mind was stellar," Gubarev said.
Gagarin sung Soviet hymns during the last checks, strapped atop the 30m-high (98 ft) rocket that would blast him into space from the long-secret Baikonur cosmodrome on the Kazakh steppe.
"Poyekhali! (Let's go!)," he cried, in a phrase that has become synonymous with Gagarin in Russia.
"The most emotional moment was when we heard he was walking and waving; his arms and legs were whole. We understood in one sigh that our five to six years of hard work had paid off and we had achieved something huge," Grechko said.
The United States responded 10 months later, when John Glenn made the first US orbital flight.