Cover Story | He had the reputation of never wanting to miss a party, but Russia's Boris Yeltsin somberly called it quits on New Year's Eve. Mr. Yeltsin's surprise resignation marked the end of a tumultuous reign. He was up, he was down, he hastened the end of the Soviet system, he enriched his relatives and cronies. But in the end, Mr. Yeltsin became the first Russian leader in history voluntarily to leave office before his term ended. Why?