Mr Arias has been involved in numerous diplomatic initiatives
Costa Rican President Oscar Arias has been called on to help mediate in the political crisis in Honduras.
The Nobel Peace Prize winner is regarded as one of the elder statesmen in Latin America.
Mr Arias, who was president from 1986 to 1990, returned to office in Costa Rica in 2006, promising to solve the accumulated problems in a country once dubbed the Switzerland of Central America.
He is best known internationally for his efforts to end the civil wars that raged in many of Costa Rica's Central American neighbours in the 1980s, efforts that brought him the peace prize in 1987.
The leader of a country without an army, he resisted pressure from the US to weigh in against the Sandinistas in Nicaragua and intervened against the activities of US-backed Contras on Costa Rican territory.
In 1987, the leaders of Nicaragua, El Salvador, Guatemala and Honduras signed a peace plan devised by Mr Arias.
Mr Arias returned to the presidency 20 years after his first stint, with a narrow victory over his opponent.
He promised to tackle poverty and sign the Central American Free Trade Agreement (Cafta) with the US. Costa Rican voters narrowly approved the agreement in a 2007 referendum.
Mr Arias was born in 1940 into a wealthy coffee-growing family.
After studying in the US, he read law and economics at the University of Costa Rica and later obtained a PhD in economics at the University of Essex, in the UK.
As a student he became a member of the National Liberation Party (NLP), soon becoming a prominent figure within the organisation.
In 1972, Mr Arias was appointed National Planning and Economy Minister. By the end of the decade he had risen to the position of general secretary of the NLP.
He was elected president in 1986, winning 52% of the votes.