Sheikh Tamim, aged 34, has not appointed a crown prince since he ascended the throne in June 2013 after his father abdicated in his favour.
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Sheikh Abdullah bin Hamad al-Thani was head of the royal cabinet and in July 2013, the new ruler of the gas-rich state appointed him as deputy head of the powerful Qatar Investment Authority, headed by Tamim himself.
The QIA, the gas-rich gulf emirate's sovereign wealth fund, has invested billions of dollars in businesses ranging from Germany's Volkswagen to French energy giant Total, Britain's Sainsbury's supermarket chain and Barclays Bank.
Its assets are estimated at $100-$200 billion (150 billion euros).