The nation's fastest-growing brokerage has attracted four million users. :
Baiju Bhatt started Robinhood with close friend Vlad Tenev in 2013 after being inspired by the Occupy Wall Street movement. The pair now sits atop the nation's fastest-growing brokerage, worth north of $5 billion. (Photo courtesy of Robinhood) Robinhood, which offers a free trading service, confirmed a new funding round on Thursday that quadruples its valuation to $5.6 billion and makes it one of the most richly-valued startups in the country.