After publishing One Day in the Life in the Soviet Union, Solzhenitsyn defected to the United States and exposed the horrific conditions behind the Iron Curtain. Though it's hard to believe today, many Western intellectuals embraced the Soviet experiment even up to that time. However, Solzhenitsyn's courage to tell the truth of the ill-fated Russian communist experiment played a key role in the thaw of the Cold War and the fall of the Soviet Union.
Be sure to read his 1978 Harvard address. Also check out the Solzhenitsyn Reader. And here is a lengthy eulogy from the New York Times.
(I received the news via telephone from Tokyo - thanks for the tip, Josh.)