Not only is China the most populous country, it is also perhaps the fastest growing–and also the largest Economy, following the US. It is part of the BRICs (Brazil, Russia, India and China), four Developing Economies that are the most populous, have the largest land mass (meaning Natural Resources) and appear to be among the fastest-growing.
China, however, tends to receive the most notoriety, perhaps due to its strategic place in the Pacific Rim. Additionally, it is important because it has taken-on the mantle of the next country to confront the US, economically, militarily and politically.
There are a number of Chinese companies that trade in the US through ADRs (American Drawing Rights) listed on major US stock exchanges. Likewise, some of the largest overseas mutual funds and ETFs enable investors to invest in China. But, for years, the transparency of corporate information, regarding many Chines companies, has been highly suspect.
Check the linked article, S.E.C. Sues SinoTech Energy of China for Fraud, from the NY Times regarding this controversy for further information.