Fox News anchor Chris Wallace describes the most important moment of his career

When Chris Wallace looks back on his most memorable moments during his tenure as host of "Fox News Sunday," he always comes back to one interaction.

In 2006, Wallace sat down with President Bill Clinton, in what was the president's first-ever interview on "Fox News Sunday."

The Fox anchor asked Clinton why he didn't do more to go after Al Qaeda mastermind Osama bin Laden. Clinton responded with a vigorous defense - an 11-minute-long tirade partially aimed at Wallace.

"You've got that little smirk on your face, you think you're so clever, but I had a responsibility for trying to protect this country. I tried and a failed to get bin Laden, I regret it, but I did try," Clinton said.

Speaking with Business Insider on the eve of "Fox News Sunday's" 20th anniversary, Wallace described his infamously tense interview with Clinton.

"I suspect it will probably be in my obit," Wallace said of the interview.

"It was a kind of surreal moment," he continued, "because I went in expecting a very businesslike interview, and I didn't think this was a particularly adversarial question."

A famously magnetic retail politician, Clinton has occasionally made headlines with his vigorous defense of his record and that of his wife, Democratic presidential frontrunner Hillary Clinton.

Wallace said the interview was important because it showed a much more aggressive, confrontational side of the president that hadn't been seen much publicly during his time in office and public life.

"This was the first time that it had been seen in public," Wallace said of Clinton's aggressive response.

"When I later asked people who had been in the White House with Clinton, they said, 'Oh yeah, we used to call it purple rage,'" he added. "It would be like a thunderstorm - it would brew up, it would grow, it would thunder and lightning and pour, and then it would pass."

Watch part of the interview below: