Friedman was the most influential economist of the last half of the 20th century. His ideas influenced presidents and prime ministers, transformed monetary policy in the United States and informed ordinary Americans' understanding of the free market.

I met Milton Friedman 16 years ago when I was asked to moderate a reprise of his popular TV series, "Free to Choose." We began shooting the new discussion series to accompany "Free to Choose" in 1990 under the direction of Bob Chitester, who had also produced the original series a decade earlier.

Since I had never met Dr. Friedman, I was invited to tea at the Friedmans' San Francisco apartment in advance of the first day's filming. I was staying a short distance away, so Rose Friedman suggested I walk rather than take a taxi, noting casually that there was a "little hill" to climb on the route from my hotel.

I arrived at the apartment huffing and puffing from the walk up the steepest hill I'd ever climbed outside the Rockies. Both Milton and Rose Friedman apparently hiked the hill on a daily basis when they were in the city, despite being nearly 80 years old at the time, while I could barely survive a single trip at half their age. They were vigorous in body and mind, as I was to discover in delightful discussions over the next week.

Unlike many famous and influential people I've met, Milton Friedman was more interested in learning about his guest than in talking about himself. He wanted to know how I had come to abandon liberalism, since he knew I had worked for a legendary union president, the American Federation of Teachers' Al Shanker, whom he had debated on the original "Free to Choose" series. I explained that foreign policy had driven me from the Democratic Party but that I had also come to favor more conservative economic policies.

"I have to write a check every quarter to pay my taxes because I'm self-employed," I said. "If more Americans had to do that instead of having the money automatically deducted from their paychecks, people would quit thinking of taxes as the government's money rather than their own. We'd have a huge tax revolt," I asserted.

Suddenly I heard Rose's voice from the kitchen. "See, I told you what mischief you were causing," she hollered, as Milton broke into a deep-throated laugh.

"The withholding tax was my fault," he explained. Apparently, as a young economist working for the Treasury Department, Friedman helped design the federal withholding tax. It was not a totally indefensible act though, he said. "Without it, we would not have had a steady flow of money into the Treasury to fight World War II."

Rose seemed affectionately unconvinced. The moment captured what I observed over the course of our conversations: an incredible relationship between two brilliant, strong-willed persons. Theirs was a true collaboration built on deep mutual respect and love.

Milton Friedman may be best remembered for his theory that money supply and interest rates are more important in contributing to a healthy economy than government fiscal policy. At the time he began writing about monetary policy, the theories of British economist John Maynard Keynes, who believed government spending could stimulate the economy, were widely accepted.

But it was Friedman's championing of the free market — along with his ability to translate complicated economic theories into plain English and communicate them to a broad audience — that made him such a formidable public figure. He was, above all, a great teacher. The world is a poorer place with his passing.