The Ng nh Dim presidential visit to Australia from 2 to 9 September 1957 was an official visit by the first president of the Republic of Vietnam. It was part of a year of travelling for Dim, who made official visits to the United States and other anti-communist countries. As with his American trip, Dim was warmly and lavishly received during the height of the Cold War, garnering bipartisan praise from both the Liberal Party of Australia of Prime Minister Robert Menzies and the opposition Australian Labor Party (ALP).

Dim addressed the Parliament of Australia and was made an honorary Knight Grand Cross of the Order of St Michael and St George, one of the highest imperial honours that can be bestowed on a non-British subjectat the time, Australians were also British subjects. Dim did not engage in substantive political discussions with the Australian leaders and he spent most of his time at public functions. He was universally extolled by the media, which praised him for what they perceived to be a successful, charismatic, democratic and righteous rule in South Vietnam, overlooking his authoritarianism, election fraud and other corrupt practices. The Australian Catholic leadership and media were particularly glowing towards the South Vietnamese head of state. A member of Vietnam's Catholic minority and the brother of Vietnam's leading archbishop, Dim had pursued policies in Vietnam favoring his co-religionists. He exempted the Catholic Church from land redistribution, gave them more aid and job promotions, and allowed Catholic paramilitaries to attack Buddhists, who formed the religious majority.

Dim's visit was a highmark in relations between Australia and South Vietnam. Over time, Dim became unpopular with his foreign allies, who began to criticise his autocratic style and religious bias. By the time of his assassination in 1963, he had little support. Australia later sent troops to support South Vietnam in the anti-communist fight, but the bipartisanship evaporated during the mid-1960s as the ALP began to sympathise with North Vietnam and opposition to the Vietnam War grew. The ALP later withdrew support for and refused to accept refugees from South Vietnam after winning office, but on the return of the centre right Liberal-National coalition to power in 1975, Vietnamese refugees were allowed to resettle in Australia in large numbers.

Ngô Đình Diệm ( or ; Vietnamese: [ŋō ɗìn jîəmˀ] (listen); 3 January 1901 – 2 November 1963) was a Vietnamese politician. He was the final prime minister of the State of Vietnam (1954–1955), and then served as President of South Vietnam (Republic of Vietnam) from 1955 until he was captured and assassinated during the 1963 military coup.

Diệm was born into a prominent Catholic family, the son of a high-ranking civil servant, Ngô Đình Khả. He was educated at French-speaking schools and considered following his brother Ngô Đình Thục into the priesthood, but eventually chose to pursue a civil-service career. He progressed rapidly in the court of Emperor Bảo Đại, becoming governor of Bình Thuận Province in 1929 and interior minister in 1933. However, he resigned the latter position after three months and publicly denounced the emperor as a tool of France. Diệm came to support Vietnamese nationalism, promoting an anti-communist and anti-colonialist "third way" opposed to both Bảo Đại and communist leader Hồ Chí Minh. He established the Can Lao Party to support his political doctrine of Person Dignity Theory.

After several years in exile, Diệm returned home in July 1954 and was appointed prime minister by Bảo Đại, the head of the Western-backed State of Vietnam. The Geneva Accords were signed soon after he took office, formally partitioning Vietnam along the 17th parallel. Diệm soon consolidated power in South Vietnam, aided by his brother Ngô Đình Nhu. After a rigged referendum in 1955, he proclaimed the creation of the Republic of Vietnam, with himself as president. His government was supported by other anti-communist countries, most notably the United States. Diệm pursued a series of nation-building schemes, emphasising industrial and rural development. From 1957, he was faced with a communist insurgency backed by North Vietnam, eventually formally organized under the banner of the Việt Cộng. He was subject to a number of assassination and coup attempts, and in 1962 established the Strategic Hamlet Program as the cornerstone of his counterinsurgency effort.

Diệm's favoritism towards Catholics and persecution of South Vietnam's Buddhist majority led to the "Buddhist crisis" of 1963. The violence damaged relations with the United States and other previously sympathetic countries, and his regime lost favour with the leadership of the Army of the Republic of Vietnam. On 1 November 1963, the country's leading generals launched a coup d'état with assistance from the CIA. He and his younger brother Nhu initially escaped, but were recaptured the following day and assassinated on the orders of Dương Văn Minh, who succeeded him as president. Diệm has been a controversial historical figure in historiography on the Vietnam War. Some historians have considered him a tool of the United States, while others portrayed him as an avatar of Vietnamese tradition. At the time of his assassination, he was widely considered to be a corrupt dictator.