The Gulf states and the wider Middle East mourned the death on Tuesday of the emir of Kuwait, Sheikh Sabah Al-Ahmad Al-Sabah.

Sheikh Sabah, who was 91, had ruled Kuwait since 2006, and steered its foreign policy for more than 50 years. He died in the US, where he had been in hospital since July following surgery in Kuwait.

Flags flew at half staff in Kuwait, which began 40 days of mourning. “Goodbye, Emir of Humanity,” read a large banner on a street near the Kuwait stock exchange.

Saudi Arabia’s King Salman and Crown Prince Mohammed bin Salman sent their condolences to the people of Kuwait and the Al-Sabah family.

“With the departure of Sheikh Sabah, we lose a wise leader who devoted his life to the service of his country and the Islamic and Arab nations,” said the Saudi Foreign Minister, Prince Faisal bin Farhan. “We console ourselves and our brothers in Kuwait for this great loss.”

GCC Secretary-General Dr. Nayef Falah Al-Hajraf said the world had “lost the pioneer of development, always striving for good, love and peace, aiming to strengthen harmony, cooperation and solidarity among the peoples of the world, and who spared no effort for the good of all humanity.”

Dr. Yousef bin Ahmed Al-Othaimeen, secretary-general of the Organization of Islamic Cooperation, said Sheikh Sabah was a voice of wisdom and moderation. “He was one of the leaders of Kuwait who worked on its prosperity and supported its stability,” he said.

Sheikh Sabah has been succeeded as emir by his brother, Crown Prince Nawaf Al-Ahmad Al-Sabah, 83, who will be sworn in on Wednesday.

Dahim Alqahtani, a Kuwaiti politics expert, said the emirate’s policies were unlikely to change under the new emir. “I believe Kuwait will follow Sheikh Sabah’s policies, which are based on balance and bridging differences,” he told Arab News.