10. Prince Albert II, Monaco
Net worth: $1 billion
Prince Albert II of Monaco's net worth reportedly comprises one-fourth of the land he reigns over, as well as an antique car collection, shares in a Monte Carlo resort, a pricey stamp collection, and the Philadelphia-area home of his mother, Grace Kelly, which he purchased in 2016 for an estimated $754,000.
9. Emir Sheikh Tamim bin Hamad Al Thani, Qatar
Net worth: $1.2 billion
Emir Sheikh Tamim bin Hamad Al Thani took over the throne of Qatar after his father, former emir Hamad bin Khalifa Al Thani, stepped down in 2013.
The former emir's estimated net worth of $2.4 billion comes from Qatar Investment Authority, which manages the country's oil and gas reserves.
T6. Emir Sheikh Mohammed bin Rashid Al Maktoum, Dubai, United Arab Emirates
Net worth: $4 billion
Mohammed bin Rashid Al Maktoum — the vice president and prime minister of the United Arab Emirates and the emir sheikh of Dubai — has spent some of his wealth on charitable donations, such as $10 billion to create the Mohammed bin Rashid Al Maktoum Foundation, which focuses on helping future generations.
1. King Maha Vajiralongkorn, Thailand
Net worth: $30 billion
King Maha Vajiralongkorn and his family made their money from investments derived from the Crown Property Bureau, which manages the property of the crown of the Kingdom of Thailand.
He also owns the 545-carat Golden Jubilee Diamond, the world's largest cut and faceted diamond, according to TIME.