Alan Greenspan, who ran the Federal Reserve from 1987 to 2006, has died, according to NPR. He was 100 years old.

Greenspan was born March 6, 1926. He became the head of the Federal Reserve — the central bank that manages American money policy — on August 11, 1987, under President Ronald Reagan. He kept the job under three more presidents: George H.W. Bush, Bill Clinton, and George W. Bush. He retired in 2006. No other Fed leader in modern times stayed in the position longer.

During his 18 years, the American economy faced several major shocks: the stock market crash of 1987, the dot-com bubble that burst in the late 1990s, the September 11 attacks, and the housing boom that later fell apart in 2008. The financial crisis happened after Greenspan left, but people have questioned whether his decisions about interest rates and bank oversight helped cause it.

How He Handled Crises

Greenspan started just before Black Monday — October 19, 1987 — when stock prices fell more than 22 percent in one day. He decided to pump money into the banks to keep credit flowing. The market steadied within days. It was a strong early test.

In the 1990s, Greenspan became the most famous central banker in America. When he spoke to Congress, financial markets moved. Traders listened closely to what he said about interest rates. In 1996, he warned about "irrational exuberance" in the stock market — a phrase people still use today when talking about asset bubbles.

Greenspan believed central bankers should use their judgment rather than follow rigid rules. He did not trust strict formulas for managing inflation the way other central banks did. Instead, he watched many economic signals. That worked well during the strong 1990s economy. After the housing crisis, people blamed him for being too hands-off.

In 2008, after leaving office, Greenspan told Congress he had been wrong about something. He had believed banks would police themselves to protect their shareholders. That did not happen. It was an unusual admission for someone known for very careful, guarded language.

Greenspan stayed active in Washington policy long after his Fed career. Before leading the Federal Reserve, he ran his own economics consulting business. He knew philosopher Ayn Rand and remained a voice in policy debates for decades.

A Fed leader serves a four-year term and can be reappointed. Greenspan was reappointed four times, across four different presidents. That length of service gave the Federal Reserve stability, which presidents valued even when they disagreed with his rate decisions.

When he left in 2006, Ben Bernanke took over. Bernanke inherited Greenspan's strong record of controlling inflation and keeping unemployment down. He also inherited problems in the mortgage market that Greenspan had not addressed more aggressively, even though the Federal Reserve had the power to do so.

Economists will study Greenspan's impact for years. Some questions are hard to answer: whether stricter rules on risky mortgages in the early 2000s would have stopped the housing bubble without causing a recession remains unclear. What is clear is his reach. For 18 years, Greenspan was the single most powerful unelected official in the American economy.