Islam is the official religion and Arabic is the official language. The UAE's oil reserves are the sixth-largest in the world while its natural gas reserves are the world's seventh-largest. Zayed bin Sultan Al Nahyan, ruler of Abu Dhabi and the first President of the UAE, oversaw the development of the Emirates and steered oil revenues into healthcare, education, and infrastructure. The UAE's economy is the most diversified of all the members of the Gulf Cooperation Council, while its most populous city of Dubai is a global city and international aviation and maritime trade hub. The country has become less reliant on oil and gas, and is economically focusing on tourism and business. The UAE government does not levy income tax, although there is a system of corporate tax in place and value-added tax at 5% was established in 2018.