South Korea has developed into one of Asia's most affluent countries since partition in 1948. The Communist North has slipped into totalitarianism and poverty.
The Republic of Korea was proclaimed in August 1948 and received UN-backed support from the US after it was invaded by the North two years later.
The Korean War ended in 1953 without a peace agreement, leaving South Korea technically at war for more than fifty years.
The following four decades were marked by authoritarian rule. Government-sponsored schemes encouraged the growth of family-owned industrial conglomerates, known as "chaebol". Foremost among them were the Hyundai and Samsung groups.
They helped transform South Korea into one of the world's major economies and a leading exporter of cars and electronic goods.
Although the South Korean economy is now the third largest in Asia and the 13th in the world, the high levels of foreign debt held by the country's banks have left them exposed to the fallout from the global credit crisis.
A multi-party political system was restored in 1987, and President Roh Tae-Woo launched an anti-corruption campaign against both his own party and his political predecessor.
Relations with its northern neighbour remain a major concern in Seoul, particularly over the North's fragile economy and its nuclear ambitions. South Korea generally resisted international calls for sanctions against the North over its nuclear programme and pursued a "sunshine" policy of engagement in the late 1990s.
This has involved aid - including shipments of fertiliser and rice - reunions between North and South Koreans, tourist projects and economic cooperation. South Korean companies employed thousands of North Korean workers at the Kaesong industrial complex near the border.
The "sunshine" ended with the election in 2008 of conservative President Lee Myung-bak, who adopted a tougher tone towards the North in response to its failure to move on the nuclear issue.
Tensions were heightened further by a spate of Northern missile tests in 2009 and then by the sinking of the Southern naval ship Cheonan in March 2010, in which 46 sailors died.
After international investigators reported finding evidence that the Cheonan was sunk by a torpedo from a North Korean submarine, South Korea stopped all trade between the two states. Pyongyang rejected the claim as "fabrication" and retaliated by cutting all relations with Seoul.
A serious cross-border clash in November 2010, as a result of which the South Korean military was placed on its highest non-wartime alert, threatened to set relations back even further.
The demilitarised zone (DMZ) between South and North Korea is the world's most heavily-fortified frontier. But the US, which maintains tens of thousands of soldiers in South Korea, is pulling its forces away from the front line and plans to hand over wartime operational control to the South Korean military in April 2012.
* Full name: The Republic of Korea
* Population: 48.9 million (World Bank, 2010)
* Capital: Seoul
* Area: 99,313 sq km (38,345 sq miles)
* Major language: Korean
* Major religions: Buddhism, Christianity
* Life expectancy: 77 years (men), 84 years (women) (UN)
* Monetary unit: won
* Main exports: Electronic products, machinery and transport equipment
* GNI per capita: US $19,890 (World Bank, 2010)
* Internet domain: .kr
* International dialling code: +82
President: Lee Myung-bak
South Korean President Lee Myung-bak took up office in February 2008, after having scored a record victory margin in December's presidential election.
His election pledges included promises to boost growth, cut high youth unemployment and raise competitiveness in the face of challenges from China and Japan.
He also pledged to take a tougher line towards North Korea than his predecessor and to strengthen South Korea's alliance with the United States.
Only months after the election, Mr Lee's approval ratings plummeted when he agreed to resume US beef imports - despite public fears over the safety of US beef - in order to secure a free trade deal.
However, his popularity later recovered on signs that the South Korean economy had successfully weathered the global economic crisis of 2008-9.
Mr Lee is South Korea's first president with a business background. He spent nearly three decades working for the Hyundai Group, becoming CEO at the age of 35. It was during this stage of his career that he acquired the nickname "The Bulldozer".
He entered politics in 1992 and became mayor of Seoul in 2002. In 2007, he became the conservative Grand National Party's candidate for the presidency. In April 2008, the GNP - which had been in opposition - won control of parliament.
The South Korean president holds full executive powers and the premiership is a largely ceremonial post. Mr Lee regularly reshuffles his cabinet, and there has been a change of prime minister every year since 2008.
From : BBC News