Jack Dorsey

Jack Dorsey splits his time between Twitter and Square, where he is co-founder and CEO.

Most entrepreneurs are lucky to see a single business succeeding. Jack Dorsey is watching two companies he co-founded succeed -- simultaneously. Twitter became ubiquitous in 2012, with hashtags slapped on seemingly every movie, television show, and sporting event. They became integrated into Apple software at the system level, set new records for the most tweets about a single event, and notched its 500 millionth registered account. Also: the Pope joined up. Meanwhile, payment processor Square signed an important deal with Starbucks that brings Square's seamless payment technology to more than 7,000 stores. Along the way, the three-year-old company became valued at $3.25 billion. This year, Square became Dorsey's top priority: he stepped away from day-to-day duties at Twitter and began spending the bulk of his time at his latest creation.

For more on this story, see Jack Dorsey's business model based on serendipity.

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