A more thorough explanation:

The Comptroller of the Currency is the head of the Office of the Comptroller of the Currency (OCC), which is responsible for regulating and supervising all U.S. national banks, federal savings associations, and federal branches and agencies of foreign banks. The Comptroller is appointed by the President and serves a term of five years.

• Supervise chartered banks
• Conduct on-site reviews and supervise banks' operations
• Evaluate applications made by financial institutions to be chartered as an OCC-supervised bank and ensure that their corporate structure is established and maintained in accordance with the principles of a safe and sound banking system
• Issue regulations for banks chartered under the National Bank Act and federal savings associations chartered under the Home Owners' Loan Act
• Take supervisory actions against banks that do not comply with the regulations issued by the OCC or that otherwise engage in risky practices
• Ensure fair access and equal treatment to bank customers
• Assist banks in making financial services accessible to underserved communities and consumers

For example, if a bank is not following the rules set by the OCC, the Comptroller can take action to make sure the bank changes its practices. The OCC also helps banks provide services to people who might not have easy access to banking, like people in rural areas or low-income neighborhoods.