It's a big day for Facebook's CEO Mark Zuckerberg...he turns 28-years-old today.
But here's something you might not know about him.
He's exactly half the age of the average S&P 500 chief executives.
Zuckerberg is pitching to investors across the U.S. ahead of Facebook's IPO.
But he wasn't always the most comfortable of public speakers.
Dan Simon has more.