Amazon founder and CEO Jeff Bezos is the richest person in the world, with an estimated net worth of more than $117 billion. He's been criticized for not donating more of that wealth.

The Amazon CEO is the only American among the world's five richest people who has not signed the Giving Pledge, in which participants promise to give away more than half of their wealth during their lifetimes or in their wills.

These are the donations Bezos is known to have made since becoming a billionaire in 1997.

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Amazon CEO Jeff Bezos may be the richest person, but he isn't well-known for his billion-dollar donations and philanthropic efforts like Bill Gates and Mark Zuckerberg.

Additional criticism has recently been heaped on Bezos' charitable ways, particularly after Amazon committed just $690,000 to relief efforts for the Australian wildfires last year. In 2019, Bezos' ex-wife, MacKenzie Bezos, opted in 2019 to sign the Giving Pledge, in which participants promise to give away more than half of their wealth during their lifetimes or in their wills.

However, among the five richest people in America, Jeff Bezos — who has a net worth of more than $117 billion — is the only one who hasn't signed on to the philanthropic commitment.

It's not clear why Bezos has avoided joining the Giving Pledge, an initiative started by Bill Gates and Warren Buffett almost a decade ago. His charitable history has "remained largely a mystery," The New York Times wrote in 2017 after Bezos posted a "request for ideas" for philanthropy on Twitter.

A nonprofit bearing Bezos' last name, the Bezos Family Foundation, has given millions of dollars to the Fred Hutchinson Cancer Research Center in Seattle. However, the fund is run entirely by the Amazon CEO's parents and hasn't received contributions from Bezos himself, according to Inside Philanthropy.

Additionally, Bezos had never appeared on the annual list of America's 50 largest donors until 2018, when he took the top spot with the launch of a $2 billion fund for education programs for the homeless. That donation represented about 1.3% of his net worth at the time, Quartz reported.

Here are all the major donations Bezos is known to have given to charity since becoming a billionaire in 1997: