Flamboyant premier and foreign minister Sheikh Hamad bin Jassem al-Thani, replaced in Qatar's new cabinet on Wednesday, spearheaded a dynamic policy that staunchly backed Arab Spring uprisings, mainly in Libya and Syria.
Sheikh Hamad helped turn Qatar into a regional heavyweight, hosting major meetings, as the tiny gas-rich state profited from the declining roles of such traditional players as Saudi Arabia and Egypt.
The witty politician-cum-entrepreneur is arguably the most familiar Qatari figure for the outside world, not only because he was foreign minister for 21 years, but also due to his controversial personality, which has earned him as many admirers as critics.
Never afraid to offend, Sheikh Hamad often sparked diplomatic fireworks, accusing fellow Arabs of hypocrisy if they dared criticise Qatar's contacts with Israel or its close links with the United States and its hosting of two US military bases.
He did not hesitate to take the lead among Arab states, most notably in the Libyan and Syrian uprisings.
Qatar was militarily involved in the NATO operations in Libya that led to the eventual overthrow of longtime leader Moamer Qadhafi, and actively supports rebels fighting to oust Syrian President Bashar al-Assad, whose arming he has repeatedly called for.
Sheikh Hamad used Qatar's gas wealth to support rising Islamist governments in Tunisia and Egypt, as his critics lashed out at his "chequebook diplomacy."
Born in 1959, Hamad is a distant cousin of the former emir, Sheikh Hamad bin Khalifa al-Thani, who abdicated on Tuesday in favour of his son, Sheikh Tamim.
HBJ, as he is nicknamed, held his post as prime minister since April 2007.
A member of Qatar's ruling family council, he first entered the cabinet as minister of municipal affairs and agriculture in July 1989 after serving for seven years as director of the minister's office.
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He was named foreign minister in September 1992, and has held the post continuously since then.
What ensured his steady rise to the top of the political ladder, was his unwavering support for the now ex-emir, who overthrew his own father in a June 1995 palace coup.
The new emir not only kept him on as top diplomat, but also named him as first deputy prime minister in September 2003, all the while entrusting him with the most delicate and contentious diplomatic missions.
The sharp-tongued Hamad did business with both the United States and its opponents in the region, such as Iran and Syria, before he turned against both regimes after the Syrian uprising began in 2011.
And he did not hesitate to meet Israeli officials, much as he met Palestinian leaders, including those from the Islamist movement Hamas.
Seen as open-minded and liberal, Sheikh Hamad jokes even about the criticisms levelled at Qatar by its detractors, who say the tiny state outstretches itself by posing as a regional player or mediator in political disputes.
With his characteristic wide grin and as comfortable in his traditional white dishdasha as in smart business suits, he speaks fluent English.
In addition to his political posts, he is a prominent businessman and chairs several major ventures, including Qatar Airways and the Addiyar real estate company.
He also heads the Qatar Investment Authority at a time when Qatar's gas and oil wealth is generating billions of dollars that are being invested in energy and infrastructure projects.
Overseas, he bought a penthouse near London's Hyde Park for 100 million pounds ($200 million) in 2007.
And according to recent US press reports, he bought a house near the United Nations for $35 million, a year after buying another home in New York for $47 million.
Little is known of his personal life, but Hamad reportedly has two wives and 15 children.