The Marshall Court, the time period when Chief Justice Marshall was the head of the Supreme Court (1801-1835), helped to set important examples for American law. Arguably the most important case of his tenure was the Marbury vs. Madison case.
In this case, it was ruled that the Supreme Court has the authority to deem laws unconstitutional. This example forever changed the Supreme Court because thousands of cases are based on this premise. The most important purpose of the Supreme Court now is to determine the constitutionality of issues. It all started with the Marshall court and Marbury vs. Madison.