King Bhumibol Adulyadej of Thailand, who took the throne of the kingdom once known as Siam shortly after World War II and held it for more than 70 years, establishing himself as a revered personification of Thai nationhood, died on Thursday in Bangkok. He was 88 and one of the longest-reigning monarchs in history.

The royal palace said he died at Siriraj Hospital but gave no further details.

King Bhumibol was a unifying figure in a deeply polarized country, and his death cast a pall of uncertainty across Thailand, raising questions about the future of the monarchy itself.

The military junta, which seized power in a coup two years ago, derives its authority from the king. But the king’s heir apparent, Crown Prince Vajiralongkorn, seen by many as a jet-setting playboy, is not held in the same regard as his father.