Qatar's former emir, Sheikh Khalifa bin Hamad al-Thani died on Sunday, aged 84, Qatar's state news agency QNA reported.
He ruled Qatar from 1972 until 1995 when he was deposed in a bloodless palace coup by his son Sheikh Hamad bin Khalifa al-Thani, the father of Qatar's current emir Sheikh Tamim bin Hamad al-Thani.
Sheikh Hamad handed power in 2013 to Sheikh Tamim in a rare abdication by a hereditary Gulf Arab ruler to try to ensure a smooth succession.
The US-allied state is small, with 2.5 million people, but is the world's largest exporter of liquefied natural gas, a global investment powerhouse and heavy hitter in Middle East diplomacy and international media.
Qatar will observe three days of mourning for Sheikh Khalifa, QNA said.