Lech Walesa, a shipyard worker and electrician in Soviet-bloc Poland, earned a reputation as an agitator and rabble-rouser in the 1970s for speaking out against Communist control of labor unions. Mr. Walesa was subjected to frequent firings and intense police scrutiny. But he was undeterred, continuing his fight for fairer labor laws — in particular, the right to strike — until it grew into something even he could not have expected: an independent political movement that became one of the nails in the coffin of the Soviet Union.