Bhumibol Adulyadej (Royal Institute: Phumiphon Adunyadet; Thai: ภูมิพลอดุลยเดช, pronounced ( listen); see full title below) (born 5 December 1927), is the current King of Thailand. Publicly acclaimed "the Great" (Thai: มหาราช, Maharaja), he is also known as Rama IX. Having reigned since 9 June 1946, he is the world's longest-serving current head of state and the longest-reigning monarch in Thai history. He is seen as so important by the Thai people that his ill-health has affected the markets.

Although King Bhumibol is a constitutional monarch, it is said that he has made several decisive interventions in Thai politics when there was bloodshed or when Thailand was in turmoil. He was credited with facilitating Thailand's transition to democracy in the 1990s, although he has supported some military regimes, including Sarit Dhanarajata during the 1960s and the Council for Democratic Reform in 2006-2008. During his long reign he has presided over 15 coups, 16 constitutions, and 27 changes of prime ministers.

The King is highly revered by the public, yet he is also protected by the Constitution as "inviolable". The so-called 'lèse majesté' statute was stated in the Constitution for the first time during the Rama VII reign after the quarrel between the monarch and an individual. The monarch himself then has no right to charge anyone who violates him. Anyone who is charged with insulting, or defaming him can be prosecuted. If proven guilty, the penalty is to be jailed for three to fifteen years. In his 2005 birthday speech, Bhumibol said he would not take lèse majesté seriously, and that the King can have flaws. Despite that, charges are still often significant, and can be brought by the state, or any individual, and often a person's political opponents during the turmoil.