John Polidori, author of the Vampyre, was hired as Lord Byron's personal physician and secretary. Polidori received his doctorate at only 19, one of the youngest recorded graduates of the University of Edinburgh where he studied mesmerism and wrote his thesis on sleepwalking. It was here the Burke and Hare bodysnatching scandal erupted slightly over a decade later. It is said he only became a physician in order to please his father Gaetano Polidori, translator of Horace Walpole's The Castle of Otranto into Italian. The elder Polidori had also been secretary to a literary figure, the Italian poet Alfieri.

Although Shelley and Byron prided themselves on their revolutionary principles, in practice the two aristocrats behaved very differently. They mocked Polidori for his literary pretensions and his (not unfounded) belief that he was their intellectual equal. Goaded by Byron to "play the gentleman" Polidori defiantly leapt a balcony to offer an arm to Mary Shelley (then still Percy's unmarried teenage mistress) as she toiled along in the mud. He only succeeded in spraining his ankle, much to the amusement of the other men. Polidori had a weakness for Mary and felt she was underappreciated by Shelley, whom he loathed and at one point even challenged to a duel. Mary was unmoved, however, and in her later writings seems to have been just as arrogantly dismissive of "poor Polly" as the others. Mrs. S. called me her younger brother, read a rueful note in his journal. The Shelley family may be represented in The Vampyre by Ianthe, the Greek girl victim. Percy Shelley used the name in Queen Mab issued in 1813, three years before he and Polidori met. Shelley's daughter Ianthe had been born the same year.

 

Polidori's nephew, Michael William Rossetti, brother of Christina Rossetti and Dante Gabriel Rossetti, published the diary his uncle had written in Switzerland chronicling the eventful summer of 1816 at the Villa Diodati where both The Vampyre and Frankenstein were conceived. Unfortunately, Rossetti had only a censored transcription of the diary to work from, as Polidori's sister Charlotte thought it too spicy to be seen in its entirety, and had destroyed the original. What is left gives the now familiar story of a writing contest in which Byron sketched out a vampire tale, but left it unfinished. Polidori took the germ of a story and fleshed it out , responding a lady friend's challenge that the frame was too slight for a story. At this point he was on his own as Byron had dismissed him.

When The Vampyre was first published, anonymously and without Polidori's permission, it was subtitled A Tale by Lord Byron. In order to increase sales, the editors spread rumours that Byron had murdered his mistress and had a cup made from her skull from which he would drink blood. A skull cup had been made for Byron, but from a monk's skull found at Newstead Abbey. Polidori attempted to squash a rumour that Byron was having orgies with two sisters by adding in a preface to the new edition I must, however, free him from one imputation attached to him—of having in his house two sisters as the partakers of his revels. This is, like many other charges which have been brought against his lordship, entirely destitute of truth. The sisters were, of course, Mary Shelley and Claire Clairmont. To Byron's annoyance, Goethe declared The Vampyre his masterpiece

Both Byron and Polidori were offended with the deceit and objected publicly. Byron published the fragment of his own version and the publishing house was forced to pay Polidori a small sum for rights to the work. They then republished the piece as A Tale related by Lord Byron, giving people the impression Polidori had plagiarised it. He gave up writing not long after and, after being rejected by a monastery, died at only 26. It is said he committed suicide by drinking prussic acid.

Varney the Vampire pays tribute to him with a character named Count Polidori.

Film treatments of the summer of 1816.
Gothic Labyrinth
Polidori is also a key character in both Tom Holland's Lord of the Dead, The Secret History of Byron (also published as The Vampyre) and Tim Powers' (sadly out of print) The Stress of Her Regard.
Gothic Labyrinth