Bruno Pontecorvo
en.wikipedia.org
en.wikipedia.org
It's always fascinating to see otherwise bright and competent characters end up making such bewildering decisions outside of their professions. In Pontecorvo's case, he condemned his young children to spending the rest of their lives in Soviet Russia - at a time when Stalin was still in power, no less.
It seems his son Gil eventually became a successful physicist in his own right, but I couldn't find out how the others fared. Based on my own experiences with communism, I can't imagine it was preferrable to life in the West.
Ironically, I people who grew up in the Soviet Union are the least able to understand what the communist movement meant to those outside the borders of the USSR. They're too poisoned by the reality of its day-to-day control over their lives. They can't understand that to a left-wing Jew in the Wehrmacht's gunsights, local communists looked like the only ones willing to fight the Germans to the death. To a black man in 1940's America, communists were the ones willing to stand up to the racist power structure on your behalf.
History is complicated.