BBC regional analyst
President Mikhail Saakashvili says Georgia has lost a "great patriot" with the death by accidental gas poisoning of his close associate, Prime Minister Zurab Zhvania.
Mr Zhvania was seen as a counter-balance to President Saakashvili
A biologist by education, Mr Zhvania was a leading activist in Georgia's embryonic environmental movement in the last years of Soviet rule.
He entered parliament in 1992, rising to vice-chairman of its foreign relations committee and, later, speaker of parliament.
From that seat, he exercised considerable power in a parliament riven by open warfare between allies and opponents of the then-president Eduard Shevardnadze.
Mr Zhvania, together with Nino Burjanadze and Mr Saakashvili, was one of the leaders of the "Rose Revolution" of December 2003. He was rewarded for his contribution by being nominated minister of state by President Saakashvili. And just two months later, he became prime minister.
Mr Zhvania forged an international reputation as a capable negotiator and a moderate voice from a troubled country in an unstable region. At home, he was the intellectual heavyweight of the leadership brought to power by the "Rose Revolution".
He knew and understood the machinery of power as an insider, and will be difficult to replace
In office, Zurab Zhvania was the central architect of a vast programme of reforms, aimed at boosting investment, curbing pervasive corruption and promoting integration into European political structures.
Admirable ambitions, and difficult to achieve in the country that was perhaps the closest thing to a "failed state" in the former Soviet Union.
He often emphasised reform of the police and civil service as the key to ultimate success. Many Georgians, exasperated by the constant demands for bribes from traffic police and otherwise insignificant bureaucrats, liked what they heard.
There was considerable success in recovering unpaid taxes and assets illegally held by officials from the former regime.
Mr Zhvania spoke of the need to establish a new relationship with Russia. The two separatist regions in Georgia - South Ossetia and Abkhazia - both have close ties with Russia.
Mr Zhvania said this meant no solution to Georgia's territorial problems would ever be found without Russian participation. But he also lamented Georgia's energy dependence on Russia, seeing it as giving Moscow undue influence over his country's internal affairs.
He was widely seen as a restraining influence on Mr Saakashvili, whose rhetoric, especially on the question of Georgia's separatist regions, can be highly emotional. And there were reports of deep rivalries between the two men.
Yet they never surfaced, and last summer, when clashes broke out in South Ossetia, and Georgia once again edged towards internal strife, Mr Zhvania led the efforts to find a negotiated solution with the region's leadership.
Mr Zhvania's death was apparently due to carbon monoxide poisoning, resulting from a poorly-installed heater. It is an unfortunately common way to die in this beautiful but poor country, which has been beset by energy shortages since the collapse of the Soviet Union.
Mr Saakashvili has seven days to nominate a new prime minister to parliament.
Mr Zhvania worked at the heart of two very different Georgian regimes. He knew and understood the machinery of power as an insider, and will be difficult to replace.