The Office of the Comptroller of the Currency is a bureau of the US Treasury. It grants national bank charters, examines those banks for safety and soundness, and can issue cease-and-desist orders or remove bank officers. Its remit covers lending standards, capital, and the trading books of national banks, including some very large derivatives dealers.
Traders meet it indirectly. Its quarterly report on bank trading and derivatives activity is a widely read snapshot of dealer positioning, and its rules shape how bank-affiliated brokers fund themselves.
The initials collide with occ-options-clearing-corporation, which clears listed options and has nothing to do with banking supervision. Context tells you which one a document means: options documents mean the clearing house, banking documents mean the Comptroller.
Related: occ-options-clearing-corporation, fdic, federal-reserve