John William Polidori was born in 1795 in London, England, the oldest son of Gaetano Polidori, an Italian political émigré scholar, and Anna Maria Pierce, an English governess. He had three brothers and four sisters.

His sister Frances Polidori married exiled Italian scholar Gabriele Rossetti, and thus John was the uncle of Maria Francesca Rossetti, Dante Gabriel Rossetti, William Michael Rossetti and Christina Rossetti, though they were born after his death.

Polidori was one of the earliest pupils at recently established Ampleforth College from 1804, and in 1810 went up to the University of Edinburgh, where he wrote a thesis on sleepwalking and received his degree as a doctor of medicine on 1 August 1815 at the age of 19.

In 1816 Dr. Polidori entered Lord Byron's service as his personal physician, and accompanied Byron on a trip through Europe. Publisher John Murray offered Polidori 500 English pounds to keep a diary of their travels, which Polidori's nephew William Michael Rossetti later edited. At the Villa Diodati, a house Byron rented by Lake Geneva in Switzerland, the pair met with Mary Wollstonecraft Godwin, and her husband-to-be, Percy Bysshe Shelley, and their companion (Mary's stepsister) Claire Clairmont.

One night in June, after the company had read aloud from the Tales of the Dead, a collection of horror tales, Byron suggested that they each write a ghost story. Percy Bysshe Shelley wrote "A Fragment of a Ghost Story" and wrote down five ghost stories recounted by Matthew Gregory Lewis, published posthumously as the "Journal at Geneva (including ghost stories) and on return to England, 1816", the journal entries beginning on August 18, 1816. Mary Shelley worked on a tale that would later evolve into Frankenstein. Byron wrote (and quickly abandoned) a fragment of a story, Fragment of a Novel, about the main character Augustus Darvell, which Polidori used later as the basis for his own tale, "The Vampyre", the first vampire story published in English.

Dismissed by Byron, Polidori travelled in Italy and then returned to England. His story, "The Vampyre", which featured the main character Lord Ruthven, was published in the April 1819 issue of New Monthly Magazine without his permission. Whilst in London he lived on Great Pulteney Street (Soho). Much to both his and Byron's chagrin, "The Vampyre" was released as a new work by Byron. Byron even released his own "Fragment of a Novel" in an attempt to clear up the mess, but, for better or worse, "The Vampyre" continued to be attributed to him.

His long, Byron-influenced theological poem The Fall of the Angels, was published anonymously in 1821.

He died in London on August 24, 1821, weighed down by depression and gambling debts. Despite strong evidence that he committed suicide by means of prussic acid (cyanide), the coroner gave a verdict of death by natural causes.

His sister Charlotte made a transcription of his Diaries, but censored "peccant passages" and destroyed the original. Based only on the transcription, The Diary of John Polidori was edited by William Michael Rossetti and first published in 1911 by Elkin Mathews (London). Reprints of this book, The diary of Dr. John William Polidori, 1816, relating to Byron, Shelley, etc. was published by Folcroft Library Editions (Folcroft, Pa.) in 1975, and by Norwood Editions (Norwood, Pa.) in 1978. A 2009 edition has recently been printed by Cornell University.

Novels

He appears as a minor and unsympathetic character in the Tim Powers horror novel The Stress of Her Regard (1989), in which Polidori does not write about vampires but becomes directly involved with them.

Paul West's novel "Lord Byron's Doctor" (1989) is a recreation, and ribald fictionalization, of Polidori's diaries. West depicts him as a literary groupie whose attempts to emulate Byron eventually unhinge and destroy him.

Polidori is a central character in the novel The Merciful Women (or Las Piadosas in the original Argentine edition) by Federico Andahazi. In it, he receives The Vampyre written by the fictional character of Annette Legrand, in exchange for some "favours".

Polidori is also a central character in the novel Gothic Romance (or Bravoure in the original French edition) by Emmanuel Carrère which, amongst other things, presents a fictionalised account of the events of 1816. Polidori is also the 'hero' of the novel Imposture (2007) by Benjamin Markovits.

Polidori is again a central character in Peter Ackroyd's novel The Casebook of Victor Frankenstein.

Polidori also appears as an enemy of Lord Byron (who is a vampire) in Tom Holland's novel Lord of the Dead and as a character in Howard Brenton's play Bloody Poetry (though for some reason Breton calls him William.)

Film and television

A number of films have depicted John Polidori and the genesis of the Frankenstein and "Vampyre" stories in 1816.

• Gothic, directed by Ken Russell (1986)
• Haunted Summer directed by Ivan Passer (1988)
• Remando al viento (English title: Rowing with the Wind) directed by Gonzalo Suárez (1988)

His name was also used for a character in a television movie adaptation of Mary Shelley's novel: The True Story, directed by Jack Smight (1973).

Dr. John Polidori was the antagonist of "The Post-Modern Prometheus", an X-Files episode from the fifth season; he was portrayed by John O'Hurley.

In the The Series episode "The Modern Prometheus", which featured Lord Byron, one of the series regulars, Methos, serves as a stand-in for Polidori. Methos, who was Immortal, was Byron's mentor, friend and physician, and experienced the same events as the real Polidori did on that (in)famous night.

Also a regular character in the stop-motion animated series Mary Shelley's Frankenhole, where Polidori is portrayed as the immortal lab assistant of Dr. Victor Frankenstein.