The secret wealth of the world's richest oil billionaires

In a 2012 dossier, Former Deputy Prime Minister Boris Nemtsov (later murdered) claimed that the Russian president owns a total of 20 palaces, four yachts and 58 aircraft.

"In a country where 20 million people can barely make ends meet, the luxurious life of the president is a brazen and cynical challenge to society from a high-handed potentate," he said, according to the Telegraph.

But according to Putin himself, his wealth is not measured in money. In Steven Lee Myers' book The New Tsar, Putin is quoted as saying: "I am the wealthiest man not just in Europe but in the whole world: I collect emotions."

"I am wealthy in that the people of Russia have twice entrusted me with the leadership of a great nation such as Russia. I believe that is my greatest wealth."

Azerbaijan

In 2003, Ilham Aliyev became the newly elected president of Azerbaijan. Thirteen years later, his name appeared in the Panama Papers – a massive leak of financial documents from the Panama-based law firm Mossack Fonseca, which revealed the shady financial dealings of some of the world's most powerful political figures.

Months before the October 2003 presidential elections in Azerbaijan, Fazil Mammadov, Azerbaijan's tax minister, began paperwork to form AtaHolding – a company that has become one of the nation's largest conglomerates. It holds interests in telecommunications, construction, mining, and oil and gas for a total value of $490 million, according to the last filings in 2014.

A second entity – this time a foundation – called UF Universe holds more assets, but Panamanian laws regarding the confidentiality of foundations are strict, which makes uncovering dollar amounts difficult.

Aliyev's two daughters and wife also have links to offshore companies managed by Mossack Fonsenca. Incidentally, Aliyev just named his wife Vice-President of Azerbaijan.

How much is the First Oil Family worth these days? No one really knows, but enough to make it onto this list.

Kazakhstan

Kazakh President-for-life Nursultan Nazarbayev was also named in the Panama Papers as a tax haven owner. He had two companies registered in the British Virgin Islands, which he used to operate a bank account with an unknown amount of funds, and a luxury yacht.