Yuri Gagarin was a Human astronaut from the Soviet Union.
In April 1961, Gagarin became the first Human in space.
In 2024, his historic feat was mentioned in the display "Manned Space Flight 1961-2024", which was seen at a gala for the astronauts of the Europa Mission. (PIC: "Two of One")
The starships USS Yuri Gagarin and VK Yuri Gagarin were named for this individual. (TNG: "The Measure Of A Man", "Up The Long Ladder")
This character was only mentioned in writing.