Jonathan Head looks back at the reign of King Bhumibol Adulyadej Thailand's King Bhumibol Adulyadej, the world's longest-reigning monarch, has died after 70 years as head of state. The 88-year-old king was widely revered but had been in poor health in recent years, making few public appearances. He was seen as a stabilising figure in a country hit by cycles of political turmoil and multiple coups.