BANGKOK — King Bhumibol Adulyadej, revered in Thailand as a demigod, a humble father figure and an anchor of stability through decades of upheaval at home and abroad, died on Thursday. He was 88 and had been the world’s longest reigning monarch.

The Royal Palace said Bhumibol died “in a peaceful state” at Siriraj Hospital in Bangkok, where he had been treated for various health problems for most of the past decade.

During a reign that spanned 70 years Bhumibol became much more than Thailand’s constitutional monarch. He was the nation’s one constant as myriad governments rose and fell, a gentle leader who used the influence of the throne to unify the nation and rally troops through the Cold War as Thailand’s neighbors fell under communist control. In his heyday, the frail-looking, soft-spoken man in spectacles wielded so much power and respect he was able to squelch coups and rebellions with a gesture or a few well-chosen words.

Bhumibol was viewed by many in the majority Buddhist nation as a bodhisattva, or holy being who delays entering nirvana to aid the human race.