Options Clearing Corporation
Like all clearing houses, the OCC makes sure that nobody cheats, and they check everything to be sure that it is working.  The OCC has about $100 billion US dollars of money deposited by big banks and trading companies (or "members").  Each day, the big banks and trading companies use the OCC to trade billions of dollars worth of stocks and other equity derivatives.  In 2015, they had 4.2 billion trades.  That was the third highest in their history.