U.S. Securities and Exchange Commission (SEC) Chairman Mary Schapiro is stepping down Dec. 14 after almost four years as head of the nation’s regulator, MarketWatch reported.

Schapiro, who was appointed on Jan. 20, 2009, presided over the agency during a period when it was responsible for implementing the Dodd-Frank Wall Street Reform and Consumer Protection Act, which became law in the wake of the financial crisis of 2008.

The announcement of her resignation came shortly before President Barack Obama said he was appointing Elisse Walter, a current SEC commissioner, as chairman.

Under Schapiro’s helm, the agency has implemented three-quarters of all the rules required by the sweeping Dodd-Frank law. The SEC also has brought a record number of enforcement cases, including 735 actions in 2011 and 734 actions this year. That record includes prosecuting what regulatory experts contend is the largest insider trading scheme ever discovered.

However, Schapiro failed to implement new rules for the $2.7 trillion money market fund industry. Schapiro, who has been a chief regulatory advocate for new money fund rules, acknowledged in August that she didn’t have the votes on the five-member commission to move forward with a plan of her own to impose further regulation of the industry. Read more.