Daniel John Morgan (3 November 1949 – 10 March 1987) was a British private investigator who was murdered with an axe in a pub car park in Sydenham, London, in 1987. Despite several Metropolitan Police investigations, arrests, and trial, the crime remains unsolved. An independent review into the handling of the investigation of Morgan's killing was published in 2021; it found that the Met Police had "a form of institutional corruption" which had concealed or denied failings in the case.

At the time of his death, Morgan worked for Southern Investigations, a company he had founded with his business partner Jonathan Rees. Rees was arrested in April 1987 on suspicion of murder along with Morgan's future replacement at Southern, Detective Sergeant Sid Fillery, and two brothers, Glenn and Garry Vian. All were released without charge. Over the next three decades, several additional police inquiries were conducted. In 2009 Rees, Fillery, the Vian Brothers and a builder, James Cook, appeared at the Old Bailey charged with Morgan's murder. The trial collapsed in 2011 after evidence obtained from supergrasses was deemed inadmissible by the court. Shortly after the case, the activities of Rees – as a private investigator – became the centre of allegations concerning the conduct of journalists at the now-defunct News of the World newspaper.

In 2006 Morgan's unsolved murder was described by Jennette Arnold, a former Labour Co-op politician who served as chair of the London Assembly, as a reminder of the culture of corruption and unaccountability within the Metropolitan Police. The profile of the case has been raised by investigative journalist Peter Jukes, who released a podcast and book about the murder in conjunction with Alastair Morgan, Daniel's brother.

Daniel Morgan was born on 3 November 1949 in Singapore, the son of an army officer. He grew up with an elder brother and younger sister in Monmouthshire, Wales, where he attended agricultural college in Usk before spending time in Denmark^[when?] gaining experience of farming.

Morgan had an exceptional memory for small details, such as car registration numbers, and in 1984 he set up a detective agency, Southern Investigations, in Thornton Heath, southern Greater London.

He married in his late twenties and moved to London, where he and his wife settled and had two children. At the time of his murder, Morgan was having an affair with a woman named Margaret Harrison, and had met her at 6:30 pm at a wine bar in Thornton Heath shortly before the murder.

On 10 March 1987, after having a drink with Jonathan Rees (his partner in Southern Investigations) at the Golden Lion pub in Sydenham, 37-year-old Morgan was found dead in the pub car park next to his car.

DS Sid Fillery, based at Catford police station, was assigned to the case, but did not reveal to superiors that he had been working unofficially for Southern Investigations. In April 1987, six people, including Fillery and Rees, Rees' brothers-in-law Glenn and Garry Vian, and two Metropolitan Police officers, were arrested on suspicion of murder. All were eventually released without charge.