Founder and CEO, Square; co-founder and executive chairman, Twitter
40 Under 40 rank: 4
Twitter user name: @Jack
Number of followers (as of Oct. 9, 2012): 2,139,737
Our favorite tweet: I work well at 35,000 feet. Just wrote 84 personal emails.
They're the hottest young stars in business across the globe. They're innovators, disrupters, and job creators; in fact, it's a pretty safe bet you're going to be working for them someday -- if you aren't already!
