6. Mark Zuckerberg
> Company: Facebook Inc.
> Value of shares: $18.7 billion
> CEO since: 2004

Mark Zuckerberg founded Facebook at Harvard in early 2004, along with help from classmates Chris Hughes, Dustin Moskovitz and Eduardo Saverin. By the end of the year, the site had more than a million users. From there, Facebook only continued to grow in popularity. By October 2012, according to the company, Facebook had more than a billion users. Along with the company’s growth, Zuckerberg’s wealth has grown as well — he was worth nearly $19 billion at the end of the last fiscal year. But not all news about the company has been positive. Most recently, the company’s initial public offering was deemed a monumental failure. Facebook Inc. (NASDAQ: FB) initially was valued at more than $100 billion, yet shares fell immediately after the IPO and did not regain their initial valuation until about a year later.

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7. Harold Hamm
> Company: Continental Resources Inc.
> Value of shares: $13.8 billion
> CEO since: 1967

Harold Hamm is the CEO of Continental Resources Inc. (NYSE: CLR), one of the nation’s largest oil exploration and production companies. He has served in this role since 1967 when he founded Shelley Dean Oil Co., the predecessor company to Continental. The company is a major player in the Bakken area, and it was the largest leaseholder in the region at the end of 2012. Because of his role in the oil industry, Hamm was named to the Time 100 list of the world’s most influential people in 2012. Oklahoma Senator James Inhofe honored Hamm for Time magazine: “Through the use of hydraulic fracturing and other new technologies, Hamm, 66, has created hundreds of jobs and homegrown energy.”

8. Rupert Murdoch
> Company: Twenty-First Century Fox Inc.
> Value of shares: $10.4 billion
> CEO since: 2013

The 82-year-old CEO and co-founder of Twenty-First Century Fox Inc. (NASDAQ: FOXA), Rupert Murdoch spent more than six decades building his multinational media empire. In June, the company split from News Corp, the publishing division responsible for publications such as The Wall Street Journal, in part due to losses in its print newspaper operations. The split came in the wake of the widely publicized phone-hacking and bribery scandal within the defunct British newspaper News of the World, which was controlled by News Corp.

9. Steve Ballmer
> Company: Microsoft Corp.
> Value of shares: $10.4 billion
> CEO since: 2000

Steve Ballmer was one of Microsoft’s first business managers, having joined the company in 1980. Microsoft Corp. (NASDAQ: MSFT) is the global leader in software products. Best known for its Windows operating system, the company recently has begun a transformation into a devices and services company, signaled by its recent purchase of Nokia’s handset business. Since being named CEO in 2000, Ballmer’s tenure has often been criticized. During his time as CEO, Ballmer more than tripled the headcount from 39,000 to more than 131,000, including Nokia employees, according to Reuters. Over the same time, Microsoft’s share price dropped more than 40%. Last month, Ballmer revealed his intention to retire in the next year.

10. Richard Kinder
> Company: Kinder Morgan Inc.
> Value of shares: $8.5 billion
> CEO since: 1999

Richard Kinder, who co-founded Kinder Morgan Inc. (NYSE: KMI) in 1997, has helped grow the business into the nation’s largest midstream oil company. Today, Kinder Morgan has more than 11,000 employees, as well as roughly 80,000 miles of pipelines and 180 terminals, according to its website. While Kinder is paid just $1 a year, his stake in the company is worth more than $8.5 billion. His company also serves as a general partner in several master limited partnerships — publicly traded stakes in energy infrastructure that offer investors favorable tax treatment.