Comment by batmenace

Not quite. Citadel is a very well known quant hedge fund. The main way Robinhood makes money (and can let people trade without commission) is by selling their customers order flow (legally) to Citadel. Citadel (legally) uses this customer information to, in the milliseconds before the customer, front-run the trade, buy the shares and sell them to the Robinhood users at a marginal profit.