Standard & Poor's introduced its S&P 500 in 1957, although the company developed its original index of 233 companies in 1923. The 1957 S&P 500 tracked the performance of 425 industrial corporations, 60 utilities and 15 railway companies, according to Reuters.
The company introduced a composite price index in 1926 as a way to track the stock market's overall performance, as reported by Reuters. The index still provides a more comprehensive snapshot of U.S. markets than the Dow Jones industrial average, which tracks only 30 companies. In 1968, the S&P 500 index closed above 100 for the first time. As of 2015, the S&P 500's worst daily loss was the Black Monday crash of Oct. 19, 1987.