Reid Hoffman is the only business leader on our list with no full-time job. As his multiple titles suggest, he represents a new kind of power broker, distinguished more for catalyzing
an entire business sector than for building any particular enterprise. Hoffman made his first fortune at PayPal and came up with the idea for LinkedIn. He now owns more than 20% of
LinkedIn's stock. CEO Jeff Weiner actually runs the giant professional networking site. Beyond LinkedIn, Hoffman has emerged as a major impresario of the social web thanks to his other
job as an angel investor and VC at Greylock Partners. He's currently an adviser, investor, or director at Zynga, Mozilla, Digg, Facebook, Flickr, and several other Silicon Valley
companies. Hoffman's brand of leadership might seem foreign to the likes of Jack Welch or Alfred P. Sloan, but it works well in a world where horizontal networks increasingly trump
vertical bureaucracies. Connect with him if you can.