monarch
mon·arch
noun
1.a hereditary sovereign, as a king, queen, or emperor.
2.a sole and absolute ruler of a state or nation.
Longest serving Monarchs
King Bhumibol Adulyadej aka Rama IX Reign: June 9, 1946 – present (67 years)
Born: 5 December, 1927
Queen Elizabeth II Reign: February 6, 1952 – present (61 years)
Born: April 21, 1926
Tuanku Abdul Halim Mu'adzam Shah, Sultan of Kedah and Yang di-Pertuan Agong
Reign: 14 July 1958 – present (55 years)
Born: 28 November 1927
Sultan Hassanal Bolkiah Reign: October 5, 1967 – present (46 years)
Born: July 15, 1946