The world's longest serving prime minister, Prince Khalifa bin Salman Al Khalifa of Bahrain, has died aged 84.
Prince Khalifa, who took office after Bahrain gained independence in 1971, had been receiving treatment at a hospital in the US, state media said.
He was an uncle to King Hamad and had a powerful role within the royal family.
The prince was regarded by some as a hardliner, and his removal was demanded by pro-democracy protesters during a failed Arab Spring uprising in 2011.
He said the Arab Spring had brought only "death, chaos and destruction", and denied claims that he had blocked political reform efforts in Bahrain.
Analysts say the choice of his successor will signal whether Bahrain, which recently agreed to normalise relations with Israel, is looking to chart a new course.