USSR Cosmonaut Left In The International Space When The Soviet Union Dissolved

On May 18, 1991, cosmonaut Sergei Krikalev departed Earth for the Soviet space station Mir. While he was up there, the country that had sent him ceased to exist, making Krikalev – for a few months at least – the "last Soviet citizen".

he was selected as a cosmonaut, and spent years in training, working on everything from repair of the space station to conducting spacewalks.
Unfortunately, his training didn't incorporate what to do when you are left in space with no official space organization (or country), which on his 1991 mission aboard Mir would have been much more useful.