They were called Plastic People of the Universe. As rock bands go, they were one of the bravest you'll ever encounter. This is from a piece entitled Czech Republic: Rock ‘n Roll Revolution or How a Psychedelic Rock Band Freed a Country from the Tyranny of Communism.
Many rock bands sing about revolutions and change, but few ever have a direct hand in such matters. The Plastic People openly defied the Communist Party in the name of art. An article written by Joseph Yanosik from online publication Perfect Sound Forever expresses the romantic importance of the band to Czechoslovakian development:
The amazing history of the Plastic People is so crucially intertwined with the history of Czechoslovakia that one can not fully understand the history of that country without knowing the history of the band, and vice versa. No other rock band has had to put up with the abuse and the obstacles that the Plastics did during their lifetime. Yet they did not plan to risk their lives for their music. As Hlavsa said, they were “dissidents against their will.” Eventually, however, they came to the realization that what they were doing was historically important and their very existence through the hard times their country was experiencing was a powerful symbol of freedom to the younger generation of Czechs [ii].