RenTech, D.E. Shaw and several thousand quant firms. https://www.technologyreview.com/s/600695/will-ai-powered-hedge-funds-outsmart-the-market/
The thing about Quant/HFT is that they're not making money by betting on the market direction. Rather they micro-scalp by getting in front of the order queue and just skimming off the froth on millions of orders. To me, that's cheating, not trading.