Mr. Alan Greenspan ended his 18-year tenure as chairman of the U.S. Federal Reserve Board this week, stepping down after the Fed raised interest rates to their highest level in nearly five years.

Mr. Greenspan is widely regarded as an icon who navigated the U.S. economy through treacherous shoals. Still, he bequeathed his successor some troubling legacies that threaten the economy and may yet tarnish his legendary image.

Only a few weeks after Mr. Greenspan took the helm at the Federal Reserve in 1987, the U.S. stock market marked the biggest fall in its history, even worse than the crash of 1929. The chairman weathered this test by drastically cutting interest rates, which helped stabilize the U.S. economy and that of the world. A few years later, Iraq invaded Kuwait and the world responded with the first Persian Gulf War. Again, Mr. Greenspan's steady hand kept the U.S. economy on an even track.