The corpse of Michael in April 1943, while dressed as William Martin
Glyndwr Michael (4 January 1909 – 24 January 1943) was a homeless man whose body was used in Operation Mincemeat, the successful Second World War deception plan that lured German forces to Greece prior to the Allied invasion of Sicily. The invasion was a success, with Allied losses numbering several thousand fewer than would have been expected had the deception failed.

Michael was born in Aberbargoed in Monmouthshire in south Wales. Before leaving the town, he held part-time jobs as a gardener and labourer. His father Thomas, a coal miner, committed suicide when Michael was fifteen years old; his mother later died when he was thirty-one. Michael, homeless, friendless, depressed and with no money, drifted to London where he lived on the streets.

He was found in an abandoned warehouse close to King's Cross, seriously ill from ingesting rat poison that contained phosphorus. Two days later, he died at age 34 in St. Pancras Hospital. His death may have been suicide, although an alternative theory suggested he may have simply been desperately looking for something to eat, as the particular poison he ingested was a paste smeared on bread crusts to attract rats.

After being ingested, phosphide reacts with hydrochloric acid in the stomach, generating phosphine, a highly toxic gas. Bentley Purchase, coroner of St. Pancras District, explained, "This dose was not sufficient to kill him outright, and its only effect was so to impair the functioning of the liver that he died a little time afterwards". When Purchase obtained Glyndwr's body, it was identified as being in suitable condition for a man who would appear to have floated ashore several days after having died at sea by hypothermia and drowning.

Before Michael, finding a usable cadaver had been difficult, as indiscreet inquiries would cause talk, and it was impossible to tell a dead man's next of kin what the body was wanted for. The dead man's parents had died and no known relatives were found. The body was released on the condition that the man's real identity would never be revealed. Ewen Montagu later claimed the man died from pneumonia, and that the family had been contacted and permission obtained, but none of that was true.

On 30 April, Lt. Norman Jewell, captain of the submarine Seraph, read the 39th Psalm, and Michael's body was gently pushed into the sea where the tide would bring it ashore off Huelva on the Spanish Atlantic coast.

Attached to Michael's body was a briefcase containing secret documents that had been fabricated by the British intelligence service. The purpose was to make German intelligence (which was known to have operatives in Huelva) think Michael had been a courier delivering documents to a British general. The documents were crafted to deceive the Germans into thinking that the British were preparing to invade Greece and Sardinia, rather than Sicily, and they succeeded in doing so.

Michael's body was picked up by a fisherman and he was buried as Major William Martin with full military honours. His grave lies in Huelva's cemetery of Nuestra Señora, in the San Marco section. The headstone reads:

William Martin, born 29 March 1907, died 24 April 1943, beloved son of John Glyndwyr Martin and the late Antonia Martin of Cardiff, Wales, Dulce et Decorum est pro Patria Mori, R.I.P.

The Latin phrase translates as "It is sweet and fitting to die for one's country." In 1998, however, the British Government revealed the body's true identity. To the gravestone was added:

Glyndwr Michael; Served as Major William Martin, RM

A plaque commemorating Glyndwr Michael is now also on the war memorial in Aberbargoed. It is headed "Y Dyn Na Fu Erioed" (translation – "The Man Who Never Was").