When fixed-income proprietary trader Mark Gorton left Credit Suisse First Boston with colleague Alistair Brown in 1998 to start Tower Research Capital, the high frequency trading industry didn’t exist. Brokerages like CSFB either didn’t provide direct market access or their service was prohibitively expensive, so Tower relied on day trading firms to execute its strategies. “There was no ‘how fast is your computer?’?” recalls Gorton, who has an MS in electrical engineering from Stanford University and an MBA from Harvard Business School. “If you had a computer, you were fast.” In 2000 he and Brown launched Lime Brokerage to cater to quantitative traders like Tower. Brown left to run Lime (which was acquired by Wedbush in 2011), while Gorton focused on growing the proprietary trading business. Today, Tower has some 300 employees — mostly technologists — and trades in 80 markets worldwide across equities, fixed income, futures and foreign exchange, competing against the likes of DRW Trading Group, Getco (see Jonathan Ross, No. 5) and Virtu Financial. “You’re constantly working very hard to find incremental inefficiencies in the market,” says Gorton, 46, an avid cyclist who pedals 25 minutes each way between his home on New York’s Upper West Side and Tower’s headquarters in Chinatown.“Competition is driving this to the point where the excess returns are getting squeezed out of the markets, and high frequency trading is looking a lot more like a regular business where people invest a bunch of money in developing software and technology to make a profit.”