Sir Thomas Playford (5 July 1896 – 16 June 1981) was an Australian politician from the state of South Australia. He served continuously as Premier of South Australia and leader of the Liberal and Country League (LCL) from 5 November 1938 to 10 March 1965. Though controversial, it was the longest term of any elected government leader in Australian history. His tenure as premier was marked by a period of population and economic growth unmatched by any other Australian state. He was known for his parochial style in pushing South Australia's interests, and was known for his ability to secure a disproportionate share of federal funding for the state as well as his shameless haranguing of federal leaders. His string of election wins was enabled by a system of malapportionment and gerrymander later dubbed the 'Playmander'.

Born into an old political family, Playford was the fifth Thomas Playford and the fourth to have lived in South Australia; his grandfather Thomas Playford II had served as premier in the 19th century. He grew up on the family farm in Norton Summit before enlisting in the Australian Imperial Force in World War I, fighting in Gallipoli and Western Europe. After serving, he continued farming until his election as a representative for Murray at the 1933 state election. In his early years in politics, Playford was an outspoken backbencher who often lambasted LCL ministers and their policies, and had a maverick strategy, often defying party norms and advocating unadulterated laissez faire economics and opposing protectionism and government investment, in stark contrast to his later actions as premier. With the resignation of the LCL's leader, Richard Layton Butler, Playford became premier in 1938, having been made a minister just months earlier in an attempt to dampen his insubordination. Playford inherited a minority government and many independents to deal with, and instability was expected; he was seen as a transitional leader. However, Playford dealt with the independents adroitly and went on to secure a one-seat majority at the next election.

In office, Playford turned his back on laissez faire economics and used his negotiating skills to encourage industry to relocate to South Australia during World War II, as the state was far from the battlefield. He built upon this in the post-war boom years, particular in automotive manufacturing; although a liberal conservative, his approach to economics was pragmatic, and he was derided by his colleagues for his "socialism" as he nationalised electricity companies and used state enterprises to drive economic growth. Generally, Playford had more dissent from within his own party than the opposition centre-left Labor Party; the main obstructions to his initiatives came from the upper house, where the restriction of suffrage to landowners resulted in a chamber dominated by the conservative landed gentry. Labor leader Mick O'Halloran worked cooperatively with Playford and was known to be happy being out of power, quipping that Playford could better serve his left-wing constituents. Playford's policies allowed for the supply of cheap electricity to factories, minimal business taxes, and low wages to make the state more attractive to industrial investment. He kept salaries low by using the South Australian Housing Trust to build public housing and government price controls to attract workers and migrants, angering the landlord class. Implemented in the 1940s, these policies were seen as dangerous to Playford's control of his party, but they proved successful and he cemented his position within the LCL.

During the 1950s, Playford and the LCL's share of the vote declined continually despite economic growth, and they clung to power mainly due to the Playmander. Playford became less assured in parliament as Labor became more aggressive, their leading debater Don Dunstan combatively disrupting the previously collaborative style of politics, targeting the injustice of the Playmander in particular. Playford's successful economic policies had fuelled a rapid expansion of the middle class, which wanted more government attention to education, public healthcare, the arts, the environment and heritage protection. However, Playford was an unrelenting utilitarian, and was unmoved by calls to broaden policy focus beyond economic development. This was exacerbated by Playford and his party's failure to adapt to changing social mores, remaining adamantly committed to restrictive laws on alcohol, gambling and police powers. A turning point in Playford's tenure was the Max Stuart case in the 1950s, when Playford came under heavy scrutiny for his hesitation to grant clemency to a murderer on death row amid claims of judicial wrongdoing.

Although Playford eventually commuted the sentence, the controversy was seen as responsible for his government losing its assurance, and he eventually lost office in the 1965 election. He relinquished the party leadership to Steele Hall and retired at the next election, serving on various South Australian company boards until his death in 1981.