Hedge funds
Hedge funds, such as George Soros's Quantum fund have gained a reputation for aggressive currency speculation since 1990. They control billions of dollars of equity and may borrow billions more, and thus may overwhelm intervention by central banks to support almost any currency, if the economic fundamentals are in the hedge funds' favor.

[edit] Retail forex brokers
Retail forex brokers or market makers handle a minute fraction of the total volume of the foreign exchange market. According to CNN, one retail broker estimates retail volume at $25–50 billion daily, which is about 2% of the whole market and it has been reported by the CFTC website that inexperienced investors may become targets of forex scams.