Longest Serving Head Of State

King Bhumibol Adulyadej (Thailand) (born 5 December 1927) is the current King of Thailand having reigned since  June 9, 1946 to till date and is the world's longest-serving head of state and the longest-reigning l monarch in Thailand history

Elizabeth Alexandra Mary Elizabeth II (born April 21, 1926) is the Constitutional Monarch of 16  Sovereign States known as the Commonwealth Realms -

• United Kingdom(UK)
• Canada
• Australia
• New Zealand
• Jamaica
• Barbados
• The Bahamas
• Grenada
• Papua New Guinea
• Solomon Islands
• Tuvalu
• Saint Lucia
• Saint Vincent and the Grenadines
• Belize
• Antigua and Barbuda
• Saint Kitts and Nevis

Elizabeth became Head of the Commonwealth and queen of 7 independent Commonwealth countries: the United Kingdom, Canada, Australia, New Zealand,South Africa,Pakistan and Ceylon in 1952 when her father George VI  died. The coronation ceremony took place on June 2,1953 (held more than a year after the period of mourning that followed the death of the preceding sovereign)

 

General Haji Sir Hassanal Bolkiah Mu'izzaddin Waddaulah (born 15 July 1946) is the 29th Sultan of Brunei and the 1st PM of Brunei.Under Brunei's 1959 constitution,the Sultan is the Head of State.
 Sultan Hassanal Bolkiah became Crown Prince in 1961 and Sultan on October 5,1967 when his father Omar Ali Saifuddien III abdictated voluntarily and his coronation was held on August 1,1968

  
Margrethe II (born 16 April 1940) is the Queen Regnant(a female monarch who reigns in her own right, in contrast to a Queen Consort, who is the wife of a reigning king) of the Kingdom of Denmark
Margrethe II 's father King Frederik IX  died on January 14 ,1972  and she was was proclaimed Queen on January 15,1972.

Carl XVI Gustaf  Carl Gustaf Folke Hubertus( born 30 April 1946) is the reigningKing of Sweden since September 15, 1973( succeeding his grandfather King Gustaf VI Adolf  because his father had predeceased him)

Juan Carlos I (born 5 January 1938) is the reigning King of Spain and Juan Carlos was designated king according to the law of succession promulgated by Francisco Franco on  November 22, 1975(2 days after the death of  Francisco Franco,Spanish General and Head of State of Spain from October 1936)

Harald V (born 21 February 1937) is the King of Norway who succeeded to the throne of  upon the death of his father Olav V on January 17,1991

Beatrix(born 31 January 1938) is the Queen Regnant of the Kingdom of Netherlands when her mother Juliana abdicated on April 30,1980