Each April, Fortune releases its list of the 500 largest -- and presumably best-run -- corporations in America. This feature usually includes a bevy of stats, and this year's issue was no exception. Here's my favorite, which I'll pose as a trivia question: Which five of Fortune's 500 boast the top-performing stocks over the past decade?

Ooh! Ooh! I know! I know!
Surely you'll get at least one of the five: Apple Computer (NASDAQ:AAPL). But that was only the fifth-best performer, returning 24.6% a year over the 10 years of Fortune's study.

And the others? Topping the list is natural grocer Whole Foods (NASDAQ:WFMI), which has seen better days, but also, according to Fortune, produced 36.6% average annual returns over the 10-year period of its study. Second is soon-to-be-acquired energy producer Kinder Morgan (NYSE:KMI), at 31.6% annually. Third is Capital One (YSE: COF), at 27.4% a year. And fourth is TiVo's (NASDAQ:TIVO) mortal enemy, EchoStar (NASDAQ:DISH), which returned 24.9% annually.

So what?
I'll understand if you're a little confused at this point. After all, Foolish colleague Anders Bylund and I are waging a duel over sportswear rebel Under Armour (NASDAQ:UARM). So here's my point: Every one of Fortune's fab five is still run by a founder. So, too, is Under Armour.

Founder and CEO Kevin Plank couldn't be more committed to his company's success. He held 32.3% of the shares outstanding, while directors and officers as a whole held 56.8% as of the last proxy statement, which was filed in April. To be fair, that total included class B voting shares. But Plank has since converted some of his class B stock into class A common; he owns roughly 4% of Under Armour on that basis, which is more than Steve Jobs' stake in Apple and CEO John Mackey's stake in Whole Foods.

A few portfolio cross-trainers
Interestingly, this stock story gets better when you consider professional investors. Significant institutional owners of Under Armour include five-star funds Baron Growth, which owns 2.1% of the outstanding shares as of June, and the Fidelity Contrafund, which owns 1.3% of the outstanding shares.

Motley Fool Champion Funds pick T. Rowe Price New Horizons, which focuses specifically on emerging small caps, is also a significant owner, with a little more than 1% of the outstanding shares, according to Yahoo! Finance.

There's no telling exactly what's attracted these all-stars to Under Armour, but high-performance results during the most recent quarter couldn't have hurt. Notably, margins continued to see dramatic improvements, up 1% on the top line and nearly 3% on the bottom line. David Gardner specifically called out margin strength via a growing and popular brand when making Under Armour a pick for his Motley Fool Rule Breakers service. The shares are up nearly 10% since.

Click. Clack. Pop!
And that brings us to the problem upon which Anders will undoubtedly focus his bear bite: valuation. Under Armour's shares look expensive at 71 times trailing earnings. I'll not argue that the multiple is somehow cheap. It isn't.

Yet multiples have a way of obfuscating other factors that may lead to outsized performance. Two come to mind here. First, there's growth. Under Armour has plenty of it still to claim. Shoes alone, after all, account for a $6 billion market, and Nike (NYSE:NKE) can't serve 100% of that business. Even a sliver of that pie would dramatically improve the fortunes of Under Armour, which has yet to book $400 million in annual sales.

Second, these shares aren't yet priced for perfection. I know that sounds weird, especially after I just got finished admitting that Under Armour sports a very high multiple to earnings. The difference here is that nearly a third of the outstanding shares are sold short, which suggests that a plurality of holders believe Under Armour is remarkably overvalued.

What's that mean for you, dear Fool? Well, contrary to what Anders might tell you, unfettered growth isn't built into the stock price. If anything, there's deep skepticism over what Under Armour can accomplish, which, in turn, has kept a lid on the shares. They'll pop like a champagne cork on New Year's Eve when (not if) that skepticism is relieved.

The Foolish bottom line
I'll give last word to Foolish colleague Todd Wenning, who, as TMFPhila in Motley Fool CAPS, had this to say about the company:

Under Armour is becoming the standard apparel for athletes of all levels. Even better than the great story are the company's improving financials -- growing margins, ROE [return on equity], and revenue. Generated free cash flow in 2005. 63% insider ownership instills confidence that management is working for shareholders and not against them.

Precisely. Click-clack. Can you hear us coming, Anders?

Under Armour is one of dozens of stocks in the market-beating Rule Breakers portfolio, five of which have more than doubled. Care to find out who they are?Click hereto get 30 days of free access to the service.

Fool contributor Tim Beyers , ranked 2,361 out of 12,276 in Motley Fool CAPS , owns a pair of Nikes that he really ought to wear more. He ought to work out more, too. Tim didn't own shares in any of the companies mentioned in this story at the time of publication. Get the skinny on everything Tim is invested in by checking his Fool profile . Whole Foods and TiVo are Motley Fool Stock Advisor selections. T. Rowe Price New Horizons is a Motley Fool Champion Funds pick. The Motley Fool'sdisclosure policyis a rebel with a cause.