He has ruled Thailand since June 9, 1946.
He is the world's longest-serving head of State. Like Elizabeth II, Bhumibol is a constitutional monarch.
Hugely popular with a semi-divine status among his people, you cannot criticise or make fun of the king in Thailand, as YouTube discovered when it was briefly banned in that country for posting videos lampooning Bhumibol.
The jazz-loving king has often used his unchallenged influence to change the course of Thai politics. In 1992, he ensured that the military moved away from governance and restored democracy. A year ago, he supported the military when it overthrew businessman prime minister Thaksin Shinawatra's elected government.
A devout Buddhist, he is an activist ruler who devotes both power and wealth to change lives in rural, impoverished Thailand.
Though he is active and spry at 80, the king has been hospitalised twice in recent times. His passing would be a serious setback for the Thai people, used to his calm, reassuring presence at their helm for six decades.
Photograph: Kittiwongsakul/AFP/Getty Images
Also read: The king who smiled on Thailand