The Sun is a British tabloid newspaper, published by the News Group Newspapers division of News UK, itself a wholly owned subsidiary of Lachlan Murdoch's News Corp. It was founded as a broadsheet in 1964 as a successor to the Daily Herald, and became a tabloid in 1969 after it was purchased by its current owner. The Sun had the largest daily newspaper circulation in the United Kingdom, but was overtaken by freesheet rival Metro in March 2018.

The paper became a seven-day operation when The Sun on Sunday was launched in February 2012 to replace the closed News of the World and employed some of its former journalists. In March 2020, the average circulation for The Sun was 1.21 million, The Sun on Sunday 1,013,777.

The Sun has been involved in many controversies in its history, with some of the most notable being their coverage of the 1989 Hillsborough disaster. Regional editions of the newspaper for Scotland (The Scottish Sun), Northern Ireland (The Sun), and the Republic of Ireland (The Irish Sun) are published in Glasgow, Belfast, and Dublin, respectively. There is currently no separate Welsh edition of The Sun; readers in Wales receive the same edition as the readers in England.

The Sun was first published as a broadsheet on 15 September 1964, with a logo featuring a glowing orange disc. It was launched by owners IPC (International Publishing Corporation) to replace the failing Daily Herald on the advice of market researcher Mark Abrams. The paper was intended to add a readership of "social radicals" to the Herald's "political radicals". Of Abrams' work, Bernard Shrimsley wrote that 40 years later there supposedly was "an immense, sophisticated and superior middle class, hitherto undetected and yearning for its own newspaper.... As delusions go, this was in the El Dorado class". Launched with an advertising budget of £400,000, the brash new paper "burst forth with tremendous energy" according to The Times. Its initial print run of 3.5 million was attributed to "curiosity" and the "advantage of novelty", and had declined to the previous circulation of the Daily Herald (1.2 million) within a few weeks.

By 1969, according to Hugh Cudlipp, The Sun was losing about £2 million a year, and had a circulation of 800,000. IPC decided to sell to stop the losses, according to Bernard Shrimsley in 2004, out of a fear that the unions would disrupt publication of the Mirror if they did not continue to publish the original Sun. Bill Grundy wrote in The Spectator in July 1969 that although it published "fine writers" in Geoffrey Goodman, Nancy Banks-Smith and John Akass among others, it had never overcome the negative impact of its launch at which it still resembled the Herald. The pre-Murdoch Sun was "a worthy, boring, leftish, popular broadsheet" in the opinion of Patrick Brogan in 1982.

Robert Maxwell, a book publisher and Member of Parliament who was eager to buy a British newspaper, offered to take it off their hands and retain its commitment to the Labour Party but admitted there would be redundancies, especially among the printers. Rupert Murdoch, meanwhile, had bought the News of the World, a sensationalist Sunday newspaper, the previous year, but the presses in the basement of his building in London's Bouverie Street were unused six days a week.

Seizing the opportunity to increase his presence on Fleet Street, he made an agreement with the print unions by promising fewer redundancies if he acquired the newspaper. He assured IPC that he would publish a "straightforward, honest newspaper" which would continue to support Labour. IPC, under pressure from the unions, rejected Maxwell's offer, and Murdoch bought the paper for £800,000, to be paid in instalments. He would later remark: "I am constantly amazed at the ease with which I entered British newspapers".

The Daily Herald had been printed in Manchester since 1930, as was the Sun after its original launch in 1964. Murdoch stopped publication there in 1969, which put the ageing Bouverie Street presses under extreme pressure as circulation grew. Additionally, Murdoch found he had such a rapport with Larry Lamb over lunch that other potential recruits as editor were not interviewed and Lamb was appointed as the first editor of the new Sun. Lamb wanted Bernard Shrimsley to be his deputy, which Murdoch accepted as Shrimsley had been the second name on his list of preferences.