There have only been five Labour prime ministers since the party was established in 1900. With Tony Blair becoming the longest continuously-serving of them on 2 August, BBC News Online looks at the personalities and the achievements of his predecessors.
1924; 1929-35: James Ramsay MacDonald
Born in Lossiemouth, Morayshire, on 12 October, 1866, to a working class family, Ramsay MacDonald started his career as a pupil teacher, before becoming a clergyman's assistant in Bristol, where he joined the Social Democratic Federation.
By 1893, he was a member of the Independent Labour Party, and worked as a journalist. He became MP for Leicester in 1906.
James Ramsay MacDonald
He was seen as a distinguished thinker and in 1911 became the parliamentary Labour group chairman.
Tagged as a moderate, MacDonald was unwilling to support Britain's involvement in the First World War, making him even more unpopular and he lost his seat in 1918.
He was forgiven by the 1922 General Election and was re-elected to represent the Welsh mining constituency of Aberavon.
He became party leader, and after Tory Stanley Baldwin failed to gain a working majority in the 1923 General Election, King George V asked MacDonald to form a government in 1924.
With a minority Labour government, dependent on the good will of minor parties, MacDonald's only significant claim to fame was the Wheatley Housing Act which began a building programme of 500,000 homes for rent to working-class families.
He called a general election in October that year, but following publication of the infamous Zinoviev letter - which alleged connections between Labour and Russian communists, although later accepted to be a fraud - his party was heavily defeated.
His moderate tendencies continued and he refused to support the 1926 General Strike, arguing that strikes should not be used as a political weapon.
Labour was back in office in May 1929, again with a minority government.
MacDonald appointed Margaret Bondfield as minister for Labour - the first female cabinet minister of any party.
His government was dominated by economic crises, precipitated by the October 1929 Wall Street crash and he battled to put in place measures to try to halt rising unemployment.
The problems forced him to form a cross-party National Government with opposition leaders, losing the support of his own party, resulting in his expulsion in September 1931.
The 1931 General Election was a disaster for the Labour Party with only 46 members winning their seats. MacDonald's coalition won a large majority, but he was subsequently defeated by Emmanuel Shinwell, a popular Labour man, in 1935. He won a by-election two years later, before dying on a cruise in the Atlantic in 1937.
1945-51: Clement Richard Attlee
Born on 3 January 1883 in Putney, London, to a middle-class family, Attlee was educated at Haileybury College and University College, Oxford.
He practised law, joining the Fabian Society in 1907 and the Independent Labour Party a year later.
After serving as a major in the Great War, he entered East End politics and became mayor of Stepney in 1919.
He was elected as MP for Limehouse in 1922 and became parliamentary private secretary to Ramsay MacDonald, although he considered the 1931 National Government the greatest betrayal in British political history.
That same year he became deputy to George Lansbury, before becoming Labour leader in 1935.
With the outbreak of the Second World War, he was invited to join Winston Churchill's Conservative government in a coalition as lord privy seal, 1940-42, deputy prime minister, 1942-45, secretary of state for the dominions, 1942-43, and lord president of the council 1943-45.
After the war, Churchill called a general election in July 1945 and Labour secured a landslide victory with its manifesto: Let Us Face the Future.
The Attlee government was epitomised by its ambitiousness and radicalism, creating the National Health Service and a new national insurance scheme, the nationalisation of a number of industries and the Bank of England.
Britain joined the North Atlantic Treaty Organization (NATO) in 1949 and the Council of Europe for unity of the European peoples in the same year.
In 1950, Labour's majority was reduced. Battered by internal disputes, high profile resignations and the death of key figures, Labour narrowly lost the October 1951 General Election.
Attlee had served as prime minister for six years and 92 days - the record Tony Blair will pass on 2 August 2003.
Attlee resigned after a second defeat in 1955, but was awarded the Order of Merit, was made an earl by the Queen and received the Garter, before his death in 1967.
1964-70; 1974-76: James Harold Wilson
Born on 11 March, 1916 in Cowlersley, Huddersfield to the son of an industrial chemist, Wilson was educated at Wirral Grammar School and Jesus College, Oxford.
He worked in the civil service during the Second World War and in 1945, at 29, was elected as one of the youngest MPs for the Ormskirk constituency. He later represented Huyton on Merseyside.
He was appointed President of the Board of Trade, but resigned in 1951with Aneurin Bevan in opposition to Labour leader Hugh Gaitskell's shadow budget plans for military spending at the expense of social programmes.
After Gaitskell's unexpected death in 1963, Wilson won the party leadership, becoming prime minister in 1964.
He steered Britain away from direct military involvement in the Vietnam War and outlawed capital punishment in 1965.
Labour's majority increased to 97 in 1966 when Wilson went to the polls for a second time.
He tried to reapply for British membership of the European Community in 1967, founded the Open University and liberalised laws affecting homosexuals and obscene publications.
But harsh economic measures and the devaluation of the pound contributed to the decline in Wilson's popularity, and the Conservatives won a narrow victory in 1970.
Labour was returned to power in February 1974, with Wilson again as prime minister. He secured a narrow majority at a further election in October the same year.
Wilson held Britain's first referendum on membership of the EC in 1975. He resigned unexpectedly in 1976 and was knighted later the same year.
He remained in the Commons until he entered the House of Lords in 1983 as Lord Wilson of Rievaulx. He died in 1995.
1976-9: James Callaghan
Born in Portsmouth on 27 March, 1912, to a naval chief petty officer, Callaghan - later to be given the sobriquet "Sunny Jim" or "Big Jim" - was educated at Portsmouth Northern Secondary School, before leaving at 14.
His professional life began as a tax officer, before joining the Labour Party in 1931, and then working as a trade union official.
He became MP for Cardiff South in July 1945, later representing Cardiff South East.
He stood for the leadership after Gaitskell's death in 1963, but lost to Wilson with respectable minority support.
He was appointed Chancellor of the Exchequer in 1964 and after a long struggle, was forced to devalue the pound in 1967. He resigned, only to be recalled as Home Secretary until 1970 where his reputation was salvaged.
He sent troops to Northern Ireland to cope with the worsening violence in 1969 and earned the title "keeper of the cloth cap" for his opposition to efforts to reform trade unions.
He was appointed foreign secretary in 1974 with responsibility for renegotiating Britain's terms of membership of the European Economic Community.
When Wilson resigned, Callaghan, aged 64, defeated Roy Jenkins and Michael Foot for the leadership of the Labour Party.
A sterling crisis and economic tussles, plus the disappearance of Labour's small majority in 1977, led to dependency on the support of the Liberals.
The government finally ended in crisis after a series of paralysing trade union strikes in the late 1970s, branded by the press as the "Winter of Discontent".
The government lost a confidence motion in March, 1979 and a general election was held, with Labour heavily defeated by Margaret Thatcher's Conservative Party.
Callaghan resigned as leader in 1980 and was created a life peer.