This Tuesday, President Donald Trump met with powerful Saudi Deputy Crown Prince Mohammed bin Salman at the White House. The two men no doubt had plenty to discuss, including but not limited to regional issues in the Middle East, the threat of terrorism and oil market woes.

The meeting was notable in an another way, too. Trump is a man known for his lifelong desire to accumulate wealth and the lavish way that he puts that wealth to use. And in Mohammed bin Salman, he may have met someone rare: A foreign leader who is richer than he is.

True, the young prince isn't yet technically the head of state. He's currently second in line to the Saudi throne. However, many have noted that the 31-year-old Mohammed has been rising fast through the Saudi royal family, taking a prominent role in the kingdom's attempts to wean its economy off oil money and in the troubling war in Yemen.

But there's no doubt that the Saudi royal family is very, very wealthy. And, like Trump, the royals are known for their opulence. Mohammed's father, King Salman, is reported to have taken 506 tons of luggage on a recent trip to Asia, including two limousines and two elevators, as well as an entourage of 1,500. There are rumors that the king is hoping to sink billions of dollars into purchasing an atoll in the Maldives.

The Saud family's wealth almost certainly exceeds Trump's own net worth, which he has estimated at $8.7 billion although other sources peg it far lower. But estimating the full extent of the Sauds' wealth is surprisingly difficult.

It is not publicly known how wealthy the Saudi royals are. One widely cited estimate pegs King Salman's net worth at more than $17 billion, but working out the wealth of world leaders is a notoriously fraught business. Like Trump, many don't release documents to make the full extent of their wealth known (though this is also true of many of the mega-rich who are not involved in politics).

What makes it more complicated with world leaders is that it can often be hard to distinguish their wealth from that of the states they run. Largely for this reason, companies that compile lists of billionaires, including Forbes and Bloomberg, tend to make a point of not including world leaders in their rankings.

Some estimates do seep out, however, so we have a broad sense of who might be in Trump's wealth bracket. Like the Saudis, many are members of royal families who sit on many generations of royal wealth. In 2011, Forbes estimated that the richest was Thai King Bhumibol Adulyadej, who had wealth of $30 billion-plus that year. (Bhumibol has since died, but his wealth may have been passed on to his son, now-King Vajiralongkorn).

Other royals estimated to hold great wealth include the sultan of Brunei, Hassanal Bolkiah, with more than $20 billion, according to Forbes in 2011, and Sheikh Khalifa bin Zayed al-Nahyan of Abu Dhabi and Sheikh Mohammed bin Rashid al-Maktum of Dubai, who each had estimated wealth of $15 billion.

There are nonroyal world leaders with high levels of wealth, too, though they tend to be autocrats and the details of their wealth are murky. In 2012, the Guardian estimated that Bashar al-Assad, the Syrian president who has overseen six years of civil war, had wealth of $1.5 billion, though it could be far more if various state-related assets in the country were included. Exactly how that wealth has changed since 2012 is not clear.

While Trump isn't likely to meet with Assad anytime soon, a meeting with Vladimir Putin could soon be in the cards. Kremlin watchers have pondered the Russian president's alleged worth for years; one 2015 estimate put it at $200 billion. The Russian leader himself pegs his wealth far lower, and there is little reliable evidence either way, but it's clear Putin has led a opulent life for the 16 years he has resided at the top of Russian power. As a report by Russian dissidents noted in 2012, he has access to 43 aircraft worth over $1 billion.

Rumors have also swirled around the wealth of Chinese leaders. Bloomberg reported in 2012 that relatives of current President Xi Jinping had many millions in assets, while a New York Times investigation into the wealth of former prime minister Wen Jiabao found his relatives held at least $2.7 billion in assets. Exact figures were never confirmed by the Chinese government, and both publications faced retribution for their reporting.

It's unusual for a U.S. leader to be in this class of international wealth. Certainly, American presidents have often been rich — in today's terms, George Washington might be worth about $525 million. Not only is Trump thought to be the wealthiest U.S. president ever, but he is the only recent one to refuse to offer a fuller glimpse of his wealth by releasing his tax returns, and he stands accused of remarkable conflicts of interest. His opaque finances and their unclear relationship to the state put him in some unusual company.

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