First elected in December 2005, Evo Morales, from the Aymara indigenous group, is first president to come from the country's indigenous majority.
As a leader of a coca-growers union, he was also the first president to emerge from the social movements whose protests forced Bolivia's two previous presidents from office.
On election, he promised to govern in favour of Bolivia's indigenous majority, who had suffered centuries of marginalisation and discrimination.
An avowed socialist, his political ideology combines standard left-wing ideas with an emphasis on traditional indigenous Andean values and concepts of social organisation.
But his first move, a few months after taking office, was to begin the process of putting Bolivia's rich gas fields under state control.
By the middle of 2006, he had renationalised Bolivia's oil and gas industries.
The increased tax revenue allowed Bolivia to vastly increase its public investment and helped boost the country's foreign reserves.
With the gas money, President Morales's administration invested heavily in public works projects and social programmes to fight poverty which reduced by 25% during his government. Extreme poverty dropped by 43%.
He also pushed for a radical re-interpretation of Bolivian national identity largely through constitutional reform.
Amid protests and disputes, he won a referendum in August 2008 on whether he should stay in office, and then a few months later a referendum approved his plans for a new constitution.
It came into force in February 2009 setting out the rights of the indigenous majority, granting more regional and local autonomy to them and redefining Bolivia as a "multi-ethnic and pluri-cultural" nation.
It also set out moves for large-scale land reform, enshrining state control over key natural resources.
Bolivia's new identity was symbolised by the adoption of the whipala, a rainbow-coloured indigenous flag which is flown alongside the traditional red, yellow and green banner.
Bolivia's new indigenous voice was heard at international climate negotiations where Evo Morales argued from an indigenous perspective for greater respect for "Mother Earth".
Mr Morales's left-wing policies have worried and in some cases antagonised many middle-class Bolivians who believe he is too radical.
Opposition was concentrated in the wealthy eastern lowland province of Santa Cruz, Bolivia's economic powerhouse.
Regional leaders there led a campaign for greater autonomy, arguing that Mr Morales's socialist policies were damaging the economy.
But over the years, President Morales's relationship with the Santa Cruz business leaders has improved and there is growing respect in Santa Cruz for his growth agenda.
In December 2009 Evo Morales was re-elected president with 64% of the vote, easily defeating his conservative opponent and gaining ground in Santa Cruz.
When a referendum was held in February 2016 on allowing him to stand for a fourth term in office, it appears he narrowly lost the vote.
Although support among ordinary Bolivians remains strong, some of the indigenous leaders, environmentalists and activists who helped put Evo Morales in power have criticised him, arguing that his policies seem to favour the wealthy, light-skinned minority.
Mr Morales met opposition from indigenous groups angered by plans for a major motorway.
He had said the 300km (185-mile) road from Villa Tunari to San Ignacio de Moxos would benefit communities throughout Bolivia.
But isolated communities of Chiman, Yurucare and Moxos Indians argued the road would open their territory to illegal logging and land grabs.
Protests led Mr Morales to suspend the project.
And many Bolivians were perplexed by a more eccentric idea for change - the clock on the face of congress which was changed to run anti-clockwise and dubbed "the clock of the south".
Since coming to power, Evo Morales has forged close links with other left-wing Latin American leaders, particularly the late Hugo Chavez of Venezuela and Fidel and Raul Castro in Cuba.
But relations with the US have been strained. In 2008 he expelled the US ambassador, Philip Goldberg, accusing him of conspiring against his government, and suspended operations of the US Drug Enforcement Administration in Bolivia.
In 2013, he expelled the US Agency for International Development (USAID), accusing it of seeking to "conspire against" the Bolivian people and his government.
In New York for the UN General Assembly in September 2014, President Morales called President Obama "an imperialist".
Like Mr Chavez, he has cultivated ties with foes of the US, such as Iran.
Having come to power with a radical programme aimed at addressing the extreme social divisions and inequalities of Bolivia, he has achieved in a few short years real social gains for the majority of Bolivians who look on his as their own.
But despite Bolivia's economic advancements, the country remains one of South America's poorest countries with analysts concerned it is overly dependant on natural resources.
In the first half of 2014, natural gas and minerals accounted for 82% of export revenues.
And the government's ability to fight crime and corruption has been questioned.