Most Americans probably haven't heard the name Abigail Johnson before. That's partially due to the fact that she's said to be quite private. On top of that, the company she runs as president and CEO is Fidelity Investments, which is privately held and therefore isn't all that widely followed. That said, Johnson's company, in which she's one of the largest shareholders, touches the lives of millions of Americans. It has also made her the richest, most powerful woman on Wall Street.

Why Abigail Johnson is wealthy
Johnson's grandfather founded Fidelity Investments in 1946. He eventually turned over leadership of the business to his son Ned in 1977, and left a 49% interest in the company to his family. Johnson's share of the company is believed to be 24%, which Forbes estimated this year to be worth $13.4 billion. That makes her the 85th richest person in the world, the 11th richest woman, and the richest woman in finance, according to Forbes.

While her grandfather founded Fidelity, Johnson's father took the company to the next level. When he took over the company it had just $4.8 billion in assets. However, he transformed it from a small mutual-fund manager into a wide-ranging financial services firm. He expanded Fidelity into the retirement business, turning it into a leader in 401(k) management. He also built the company's money market-mutual fund business and its discount brokerage business. The company now has nearly $2 trillion in assets under management and millions of customer accounts. That growth pushed the Fidelity's income higher, skyrocketing the value of the company and therefore the family's net worth.

A powerful position
Fidelity is a force to be reckoned with in the financial service industry, and that fact alone makes Johnson powerful. However, the fact that she's one of the few women in the upper levels of leadership in the finance industry, which has long been dominated by men, only adds to her power. In fact, Forbes currently ranks her as the 19th most powerful woman in the world and the most powerful woman in the investment industry, while only being behind Federal Reserve Chairwoman Janet Yellen and Santander Group Chairwoman Ana Patricia Botin on the list of the most powerful woman in all of finance.

As has been famously said, "with great power comes great responsibility." That's certainly the case for Johnson: Her job is not only to take Fidelity Investments to the next level, but to serve her customers well. One way she's doing that is by creating more passively managed products such as index funds and exchange-traded funds that will provide customers with low-cost investment options. Exchange-traded funds in particular have been popular with investors, as they combine the all-day tradability of stocks with the diversification benefits of mutual funds. By moving into ETFs, Fidelity will be able to better compete with other large investment managers. That said, the key for Johnson will be to offer products that are both good for Fidelity's bottom line and in her customers' best interests.

Abigail Johnson is one of the richest people in the world as a result of her family building Fidelity into a financial services powerhouse. Few of us have the luxury of being handed the reins of the family empire; instead, we must build our own financial empire from scratch. However, we are able to easily invest in great companies and hold them for the long term in our investment accounts. This is the best way to build up our own net worth so we'll have something of value to pass down to our own families.