Sheikh Hamad's title changed to king when Bahrain switched from being an emirate to a kingdom in February 2002.
He had been crown prince since 1964, when, on the death of his father Sheikh Isa in March 1999, he became emir.
Born in 1950, he was educated at a public school in Cambridge, England, and went on to study at Mons Officer Cadet School in Aldershot, England, and at the US Army Command and Staff College, Fort Leavenworth, Kansas.
In 1968, he founded and became commander-in-chief of the Bahrain Defence Force (BDF). He served as minister of defence from 1971 to 1988.
The government has over the years faced protests from the Shia majority, with demonstrators saying the ruling Sunni minority shuts them out of housing, healthcare and government jobs.
Bahrain saw anti-government unrest in 2011 - inspired by uprisings in Tunisia and Egypt. The government used violence to try end the protests, in which some several people were killed. It also called in Saudi Arabian troops. However, protests and clashes continued into 2012.
King Philippe succeeded to the throne in July 2013 on the abdication of his father, the 79-year-old Albert II, who stepped down on grounds of health.
Born in 1960, the future King Philippe graduated from the Belgian Royal Military Academy and went on to study political science at Oxford and Stanford.
He is a trained fighter pilot and paratrooper, and was widely expected to pass over his father and succeed to the throne on the death of his uncle Baudouin in 1993. But his apparent diffidence in public led to his father becoming king after all.
Prince Philippe became Duke of Brabant and went on to marry Belgian aristocrat Mathilde d'Udekem d'Acoz. They have four children, the eldest of whom, Princess Elisabeth, is heir to the throne.
As Duke of Brabant he served as honorary head of the Belgium's Foreign Trade Agency, and flew the flag for Belgian business on dozens of high-level trade missions worldwide.
Respect for the monarchy is one of the few factors that crosses the communal divide in Belgium, and King Albert exercised his constitutional authority in advising political leaders on the formation of a government during the 2010-2011 parliamentary stalemate.
King Philippe, on the other hand, is expected to have a difficult relationship with the hardline Flemish nationalists of the Vlaams Belang, whom he has publicly criticized.
Groomed for "kingship", as his late father King Hassan II referred to his upbringing, Mohammed VI became monarch in 1999.
He initiated political and economic changes and an investigation into human rights abuses during his father's rule.
The king says the fight against poverty is a priority, earning him the name "guardian of the poor". Economic liberalisation has attracted foreign investment and officials point to better basic services in shanty towns and rural areas. But some non-government groups say little has changed, with poverty still widespread and unemployment remaining high.
A key reform has been the Mudawana, a law which grants more rights to women. The king has said it is in line with Koranic principles, but religious conservatives have opposed it.
Bomb attacks in Casablanca in 2003 prompted the enactment of new anti-terrorism laws and a reinvigorated campaign against extremists. But some rights groups say the measures have eroded human rights.
King Mohammed married computer engineer Salma Bennani in 2002. They have a son, Crown Prince Moulay Hassan, born in 2003, and a daughter, Princess Lalla Khadija, born in 2007.
Under the constitution, the king can dissolve parliament and dismiss or appoint the prime minister. After protesters demanding political reform took to the streets in February 2011, King Mohammed announced a wide-ranging review of the constitution.
He scored a landslide victory in a July 2011 referendum on a reformed constitution which he proposed to placate "Arab Spring" protests. However, although the new constitution grants more powers to the prime minister and parliament, the king still retains veto power over most government decisions.
Crown Prince Harald became king on the death of his father Olav V in 1991. Born in 1937, he fled with his mother and siblings to the United States after the German invasion of Norway in 1940, while his father and grandfather, the then King Haakon VII, joined the government in exile in London.
The royal family returned to Norway at the end of the war, and Prince Harald went on to study at the University of Oslo, the Norwegian Military Academy and Oxford University.
Like his father and grandfather, King Harald is a keen sportsman, and represented Norway with distinction as a yachtsman at various international events, including the Tokyo, Mexico and Munich Olympics.
He caused some controversy by insisting on marrying a commoner, contrary to the tradition of marrying a royal princess. He and Queen Sonja have two children, Princess Martha Louise and Crown Prine Haakon.
The king has clearly defined constitutional duties. Apart from being head of the armed forces and Church of Norway, he chairs the Council of State once a week. He appoints the government according to which party commands the largest number of seats in parliament, or else on the advice of the head of parliament and the prime minister of the day.
King Harald has cotinued the royal family's tradition of of unpretentious public duty, and serves as a symbol of the country's strong sense of national identity.
King Mswati III was crowned in 1986 at the age of 18, succeeding his long-serving father King Sobhuza II, who died at the age of 82.
The king, who is known as Ngweyama - "the lion" - often appears in public in traditional dress and has many wives.
He rules by decree and has been criticised for the heavy-handed treatment of opponents.
The king has also been criticised for requesting public money to pay for new palaces and luxury cars.
Protesters angered by economic decline have become increasingly vocal in demanding political reform.
In 2012, King Mswati - who is thought to have a personal fortune of a 100 million dollars - was given a jet aircraft as a present for his 40th birthday, reportedly a gift from friends and development partners.
King Carl XVI Gustaf ascended the throne in 1973, on the death of his grandfather Gustaf VI Adolf. The current king's father died in a plane crash in 1947, when Carl Gustav was only nine months old.
During his long royal apprenticeship, Carl Gustav underwent the usual military training, but also studied history, politics and economics at Swedish universities, served in the diplomatic corps, and worked in banking and commerce.
Constitutional changes in 1974 deprived the king of all but ceremonial duties, such as opening parliament and representing Sweden at the diplomatic level.
King Carl XVI Gustaf is best known abroad for presenting the annual Nobel Prizes.
He married in 1976, and he and Queen Silvia have three children, the eldest of whom - Princess Victoria - is heir to the throne.