Given that people are currently celebrating the 75th anniversary of start of the Spanish Civil War thought I might mention Andrés Nin.

He was leader of the POUM an allegedly Trotskyist party although Trotsky had disavowed him.

He was abducted by the Stalinists/NKVD in June 1937 and subjected to horrific torture in order to attempt to get him to confess to being fascist spy.

He was flayed alive but never signed a confession.

Franco was no angel but Spanish people did not miss anything by not having the Stalinists win.