The Securities and Exchange Commission (SEC) is the US government regulator responsible for regulating the securities markets and protecting investors.
The US Securities and Exchange Commission was created as a result of the US Securities Act of 1933 and the Securities and Exchange Act of 1934, primarily in response to the 1929 stock market crash that led to the Great Depression.
The SEC itself can initiate civil actions against offenders, and also works with the Department of Justice on criminal cases.