Final answer:
The Glass-Steagall Act was the legislation that separated commercial banking and investment banking activities until its provisions were repealed in 1999.
Step-by-step explanation:
The act that separated commercial banking and investment banking activities until 1999 was the Glass-Steagall Act. This act, enacted during the presidency of Franklin D. Roosevelt, was part of a broader legislative effort to restore confidence in the financial system after the Great Depression. Notably, it created the Federal Deposit Insurance Corporation (FDIC) to insure bank deposits and prohibited banks from engaging in both commercial banking and investment banking activities. The ultimate repeal of these provisions in 1999 is often cited as one of the factors that led to the 2008 Financial Crisis.