Grey tombstones lean against one another in the tufted grass. The ancient church tower soars over the Oxfordshire countryside. This is All Saints, Spelsbury, the quiet burial place of an unquiet soul. John Wilmot, 2nd Earl of Rochester, is one of our finest lyric poets. He influenced Pope and, at his best, matched Dryden. Yet his grave is unmarked, his memorial just a coffin plate. He had a satanic reputation, and only now are there moves to celebrate him.

After more than 300 years of being censored and anathematised, this Restoration poet is seen as a man of our times. He believed that after this life there was oblivion, in an age when not to believe in God was to be frighteningly isolated. He celebrated sexuality, from tender love to pornographic obscenity, in language that has only recently been printable in this newspaper.

This profoundly troubled and contradictory man is now and perhaps for ever Johnny Depp. In The Libertine, released on Friday, Depp creates his own Rochester, in the last years of his short life, in a performance so mesmeric that the dissolute earl could become an antihero of our times, just as he was in the 1680s. With dark, glowing eyes, lidded with world-weariness, he is a match for all who come up against him, including John Malkovich's wily King Charles II. 'You will not like me,' Depp warns in his opening speech, but by the time he concludes - 'How do you like me now?' - audiences are either weeping with pity or lost in admiration.

The real Rochester was nastier, sharper, more desperate and more creatively gifted. His father, Henry, was a hard-drinking royalist, who helped rescue the future Charles II after the battle of Worcester in 1651, and acted as surrogate parent to the 21-year-old prince during his escape to France. Henry died in 1658; his son was only 10.

Rochester's puritanical mother, Ann Lee, presided over clerical tutors who filled the boy's mind with the sinfulness of lust and the wrath of a vengeful God. But he also read classical authors whose ungodliness taught a very different lesson. By the age of 12, when he went up to Wadham College, Oxford, he was an accomplished classicist. His first year there coincided with the saturnalia of the Restoration as Charles II arrived in England with his mistress Barbara Villiers, the future Duchess of Cleveland.

After a grand tour of France and Italy, Rochester, aged 17, arrived at court on Christmas Day, 1664. Just as Henry had taken care of the future king, so Charles now virtually adopted Rochester. He gave him money and allowed him unprecedented licence to criticise him until the scars of the earl's wit became too painful to bear.

According to a contemporary, Rochester at 17 was 'a graceful and well-shaped person, tall and well made, if not a little too slender'. He was witty and scurrilous. In a court whose chief enemy was boredom, he was cherished for improvising witty rhymes that had the company convulsed with laughter. The young earl thought he could do no wrong, but within five months he was in jail. A beautiful heiress to a great fortune, Elizabeth Mallet, was being sold off by her grandfather to the highest bidder.

Since Rochester had no money, he abducted Elizabeth in a coach and six. He was stopped, and the king ordered him to the Tower of London, where he remained for one month. Eventually, Elizabeth eloped again with him, this time of her own free will, and married him in early 1667.

Samuel Pepys, seeing them six days later at the theatre, noted enviously: 'As I hear some say in the pit, it is a great act of charity, for he hath no estate.' But Rochester was by now a war hero. Anxious to show loyalty to Charles, he twice volunteered for battle against the Dutch fleet and was commended for his courage.

Once married and free to live off Elizabeth's fortune, he abandoned her to the country dullness of Adderbury, his house in Oxfordshire, and caroused in London. He became a member of 'the merry gang', a group of talented, high-born thugs and hooligans. They had come to notoriety in 1663 when Sir Charles Sedley and Lord Buckhurst gambolled naked on a Covent Garden balcony in full view of the crowds, 'acting all the postures of lust and buggery that could be imagined', as Pepys wrote indignantly.

From time to time, the merry gang groomed and procured mistresses for the king, having tested them out in advance. One of them (not in the film) was Nell Gwyn, who became the king's longest-serving mistress. Nell was a sweet soul who escaped the lashes of Rochester's verse.

None of this explains the awe in which the earl was held by his contemporaries. There was nothing unusual, then or later, about his callous promiscuity. Dr Johnson's friend James Boswell kept six mistresses, had liaisons with four actresses and recorded having sex with over 60 different prostitutes. Yet future generations made Rochester out to be more degenerate than any other figure of those times. For Dr Johnson (who believed that sensible wives should turn a blind eye to their husbands' adulteries), Rochester was the symbol of infamy. Here was the spectacle of man without God, and the lawless amorality that would follow. He read Rochester right. Rejecting God and the laws of man had begun with his classical studies. At Wadham, the Royal Society, formed from the Experimental Philosophical Club, insisted that every assumption had to be tested. Rochester tested everything to destruction: his courage, his relationships and finally his life.

On his grand tour, he admired the power and magnificence of the Catholic Church, but also the cynicism with which sins could be washed clean simply by buying a pardon. In 1665, as the English fleet closed with the enemy, two of his shipmates had premonitions of death. Rochester entered into 'a formal agreement, not without ceremonies of religion, that if either of them died, he should appear, and give the other notice of the future state, if there was any'. The two men were killed by a single cannonball. Neither reappeared. Since then, the earl had seen people dying in the great plague, the clergy conspicuous by its absence. And Archbishop Shelden kept mistresses, as Pepys recorded in his diary.()