In the early morning of Aug. 21, 1968, however, flower power was overcome by Soviet tanks. In protest, Jan Palach, a philosophy student, doused himself in gasoline and set himself on fire in Prague’s Wenceslas Square. It was, Mr. Janicek recalled, an inauspicious time to form a rock band.

The band  founded by bassist Milan Hlavsa  was initially made up of several schoolmates who covered songs by the Velvet Underground, the Doors and their beloved Zappa. Their manager was Ivan Jirous, an eccentric art critic, who became their muse in the same manner that Andy Warhol had been to the Velvet Underground. Further infuriating the Czechoslovak Communists, they sang their first songs in English, with the help of Paul Wilson, a Canadian translator.

Mr. Jirous, who was also known as Magor, roughly translated as “loony” in Czech, kept the band on a steady course of nonconformity. The band’s first studio album  recorded in 1974 and based on lyrics by the outlawed Czech poet Egon Bondy  was satirically titled “Egon Bondy’s Happy Hearts Club Banned.”

Jan Brabec, the band’s former drummer, argued that the Plastics were part of a longstanding Czech tradition of cultural rebellion. After 1968, the government’s repression of personal freedom was both so strong and so unpredictable that laughing in a darkened cinema or listening to rock ’n’ roll could become an unintentional political act. Fans who attended Plastic People performances potentially risked expulsion from college, arrest and even jail.

“To be playing music was to be free, to say you are doing what you believe and that you are willing to live with the consequences,” Mr. Brabec said.

In 1970, the Communist government revoked the license for the Plastics to perform in public, forcing the band to go underground. In February 1976, the Plastic People organized a music festival in the small town of Bojanovice  dubbed “Magor’s Wedding”  featuring 13 other bands. One month later, the police set out to silence the musical rebels, arresting dozens. Mr. Janicek was jailed for six months; Mr. Jirous and other band members got longer sentences.

Mr. Havel, already a leading dissident, was irate. The trial of the Plastic People that soon followed became a cause célèbre.