The richest people in the world have a staggering amount of wealth — comparable to the GDP of small countries for some. Many of the world’s richest, like Microsoft founder Bill Gates, Amazon CEO Jeff Bezos or Facebook co-founder Mark Zuckerberg, are self-made and turned an idea into a billion-dollar fortune. For others, like the Koch brothers of Koch Industries, their businesses were inherited, but their control of the company led to overwhelming amounts of wealth.

Many billionaires donate a large percentage of their money to charity. In fact, several of the world’s richest including Gates and Warren Buffet have made “The Giving Pledge,” which means they have vowed to give away at least half of their wealth to charity.

There are more than 2,200 billionaires in the world, Forbes reported, and that number is only expected to grow. Based on the most recent estimates from Forbes, the world’s richest people range from tech CEOs to heiresses to expert investors. Read on to find out how and why these people got so rich.

1. Jeff Bezos

Responsible for the growth of online shopping and e-commerce, Jeff Bezos made his fortune by founding Amazon.com. The 53-year-old CEO of Amazon, launched the retail giant in 1994 after leaving his New York hedge fund job. Initially an online book retailer operated out of Bezos’s garage in Seattle, Amazon.com grew to become the world’s largest online shopping retailer, now worth over $430 billion, according to CNBC.

Bezos also owns a private space company Blue Origin and purchased The Washington Post in 2013 for $250 million. Amazon bought the upscale grocery chain Whole Foods in June for an estimated $13.7 billion.

Bezos’s parents, Jackie and Mike Bezos, operate the Bezos Family Foundation, which supports youth education.

2. Bill Gates

Born in Seattle, Gates used his first computer in 1967 while a kid in school. And about a decade later, he and his childhood friend Paul Allen, who also developed an interest in computers at their school, co-founded Microsoft together in 1975.

He was Microsoft’s CEO until 2000, and was the company’s chairman and largest shareholder until 2014. Gates is still a member of the board and serves as a technology adviser for the company.

Gates and his wife, Melinda, co-chair the Bill and Melinda Gates Foundation, which is the world’s largest private charity. The foundation, launched in 1999, focuses on ending infectious diseases around the world, including HIV and malaria.

Outside of Microsoft, Gates is a public figure who, along with Warren Buffett and Mark Zuckerberg, founded “The Giving Pledge” to encourage other billionaires to donate a hefty amount of their wealth to charity. His charitable foundation focuses on health and development issues across the world.

An influential figure, the 61-year-old also releases a list of his favorite books each year.

Industry: Technology
Net worth: $90 billion

3. Warren Buffett

Berkshire Hathaway CEO Warren Buffett is an iconic figure and investment genius who bought his first stock when he was just 11 years old and filed his first taxes at age 13. Nicknamed the Oracle of Omaha, Buffett owns more than 60 companies.

One of the world’s best investors, Warren is also known for his cheap spending habits. In the recently released HBO documentary Becoming Warren Buffett, the 86-year-old billionaire said he typically pays under $4 for breakfast from McDonald’s each morning.

Like his peers, Buffett is a philanthropist and has vowed to give away 99% of his wealth.

Industry: Finance and investments
Net worth: $84 billion