"Investments perform better than investors." -- Jack Bogle

To call Jack Bogle a legend may be understating the stature of a man that's arguably done more for the individual investor than anyone else.

Is that high praise? Sure, but in a world of shockingly overpriced mutual, hedge, and private equity funds, Bogle's championing of low-cost index funds has undoubtedly made the world a safer place to invest. And he's been doing this for a heck of a long time -- in late September, Vanguard celebrated its 39th anniversary.

If you're wondering what's changed for Bogle in recent years, the answer is, not a whole heck of a lot. At 84 years young, the godfather of low-cost indexing is still on the warpath to help retail investors see the light, even as the market continues its gut-wrenching churning. In a recent interview with CNBC, Bogle said that he does watch the market on a day-to-day basis, but, as he put it, "the trick to what I've done in investing is I don't do anything." He continued, "I look, and watch, and observe, and laugh."

It's this kind of a cool head in hot markets, along with a razor-sharp focus on what really matters in investing -- notably costs and fees as well as long-term economic and business growth -- that have given Bogle such staying power. Consider what Bogle said to our own Robert Brokamp in December 2008 -- right in the depths of the financial crisis:

Today, the dividend yield is 3%... and I think from these somewhat depressed levels, over the next decade, earnings could grow. I am not saying they will, but I think it is not unreasonable to expect earnings to grow at about 7% a year, which of course means they will double in 10 years. So we have a 3% dividend yield and a 7% earnings growth and I don't look for that dividend to be cut a lot. It might be cut a little bit, but there are many companies that are doing quite well in America, outside of the financial area. So that would be a 10% investment return.

The S&P 500 (INDEX: ^GSPC) is close to a double since that conversation.

Tomorrow, Motley Fool co-founder and CEO Tom Gardner will sit down with John Bogle, and we want to know what you want to hear from the Vanguard founder. In the comments section below, submit your questions, and after the interview, we'll post the Q&A right here on Fool.com.

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Matt Koppenheffer has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.