During the height of the Cold War, the Soviet Union was not very forthcoming about their mistakes and failures. Before Colonel Gagarin’s flight, there were rumors of a cosmonaut death, but it was not until the fall of the Iron Curtain that it was revealed (officially) that Senior Lieutenant Valentin Bondarenko had burned to death in a training accident just 2 weeks before Gagarin’s historic flight.

A crater on the far side of the Moon is named after Bondarenko.

Some have speculated that if the USSR had revealed the circumstances of Bondarenko’s death, then the tragedy of Apollo 1 – where US astronauts Gus Grissom, Ed White and Roger Chaffee also burned to death on the ground – might have been avoided or mitigated.

But to directly address your question, even now that the early records of the Soviet space program have been declassified, there is no evidence that any cosmonaut was launched into space before Gagarin.

Yuri Gagarin was the first person launched into space, the first to orbit the Earth, and the first to return safely to Earth (all on the same flight: Vostok 1).

Godspeed to all the astronauts and cosmonauts who have lost their lives pursuing the exploration of space. Gratitude to all who have survived.