Sheikh Sabah was Kuwait's foreign minister for 40 years
Sheikh Sabah al-Sabah had been the de facto ruler of Kuwait for several years before he was unanimously elected the Gulf State's new emir.
The appointment was widely expected after Kuwait's parliament voted to oust his predecessor and cousin, Sheikh Saad al-Abdullah, on health grounds.
Sheikh Saad had been emir since the death of Sheikh Jaber al-Ahmed two weeks ago.
Though Sheikh Sabah is in his mid-seventies and had a pace-maker fitted in 1999, he is said to be in good health.
The fourth son of Emir Ahmed I, Sheikh Sabah al-Ahmed al-Jaber al-Sabah was born in 1929.
Sheikh Sabah was educated at the Mubarakiya School in Kuwait City before he joined the royal court of his father, who ruled between 1921 and 1950.
Kuwait's oilfields were set ablaze by Iraqi forces in 1991
He was a member of the Supreme Committee from 1955 until Kuwait ceased to be a British protectorate and gained full independence on 19 June 1961.
After serving for a year as minister of information and guidance, Sheikh Sabah was appointed foreign minister in 1963, a post he would hold for a remarkable 40 years.
Sheikh Sabah went on to earn a reputation as an able diplomat, heading Kuwait's inaugural delegation to the United Nations General Assembly later that year.
He established strong ties with world leaders, smoothed tensions with nearby Iran, and lobbied for an international response to Iraq's invasion of Kuwait in August 1990.
He also represented his half-brother internationally after Sheikh Jaber suffered a stroke in September 2001.
Groundbreaking new role
Sheikh Sabah also played an important role instigating Sheikh Jaber's domestic policies.
In February 1978, two months after Sheikh Jaber succeeded Sabah III as emir, he was appointed Kuwait's deputy prime minister.
Sheikh Jaber seldom appeared in public after suffering a stroke in 2001
But for a brief interruption following the Gulf War, Sheikh Sabah retained the post until July 2003 when the public became increasingly concerned by the failing health of the emir and Crown Prince Sheikh Saad.
Sheikh Jaber issued a landmark decree that month, separating the posts of crown prince and prime minister and appointed Sheikh Sabah as premier.
Delegated with considerable executive powers, Sheikh Sabah continued the reforms begun by the emir.
His government has appointed the emirate's first woman minister, cracked down on Islamist militants, and revised the school curriculum to promote religious tolerance.
Kuwait has also developed into a key Western ally in the Gulf, even allowing US troops to launch the invasion of Iraq in 2003 from its territory.
The emirate controls about 10% of the world's proven oil reserves and Sheikh Sabah has played a vital role as chairman of Kuwait's Higher Petroleum Council.