Voltaire, like God, whom he patronized, is always there. “No authors ever had so much fame in their own life-time as Pope and Voltaire,” Dr. Johnson dogmatized in the late eighteenth century, and though Pope still sings for those with ears to hear him, Voltaire still squabbles, a more lifelike sound, and does it everywhere. On the Op-Ed page of the Times, he can ornament Paul Krugman or offend William Safire, and he is fun to read about, no matter what he is doing. In fact, he is most fun to read about when what he is doing is doing good, since he does good without being pious, an unusual mixture. For all that he was a mad egomaniac and an unabashed self-promoter, he remains matchlessly entertaining company, incapable of either shame or shoddy thinking.

There are at least three distinct Voltaires. First is the scandalous Voltaire, who by the seventeen-twenties had become the leading controversialist in France, with a series of topically loaded plays and poems, only to be thrown into the Bastille twice for being generally annoying, and in 1726 get exiled to England, where he absorbed and wrote about English learning and English parliamentary institutions. Next, there is the scientific Voltaire, who returned to France in 1728 and eventually became the lover and disciple of the brilliant Mme. Châtelet, and who, closeted with her at her Château de Cire, wrote on math and science and did more than almost anyone else to bring the news of Newtonian physics to Europe. Then, from the seventeen-fifties until his death, in 1778, there is the socially conscious Voltaire, the Voltaire who became one of the first human-rights campaigners in Europe, and whose determination to remake the world one soul at a time W. H. Auden could still idealize in 1939, in his poem “Voltaire at Ferney.” (“And still all over Europe stood the horrible nurses / Itching to boil their children. Only his verses / Perhaps could stop them: He must go on working.”)

Although no single volume in English does justice to all the Voltaires, the second, scientific Voltaire, at least, inspired one of the most blissfully entertaining books in the language, Nancy Mitford’s 1954 “Voltaire in Love,” an account of his great affair with Mme. Châtelet and of their joint introduction to the pleasures of sex and calculus. It is de rigueur to dismiss Mitford as a reckless amateur who, as someone said, made the Enlightenment philosophes into members of her family. But they were members of her family—or more like them than they were like the kind of responsible, well-read, judicious dons, offering syntheses of current thought, beloved of academic historians. Voltaire spent his life with society people and show people, and lived in terror of boredom, not inconsistency. Mitford understands Voltaire’s mixture of bad faith, irascible egotism, genuine altruism, and sporadic courage, all played out in an atmosphere of petty literary politicking—in part because the type remains intact in France to this day.

Ian Davidson, a longtime correspondent for the Financial Times, has, in his new book, “Voltaire in Exile” (Grove; $24), taken on the story of the last Voltaire. This Voltaire evolves out of the two others; in fact, they are still right there. The old, good Voltaire was exactly the same man as the young rascal, and the rascality fuelled the goodness with energy and mischief. Yet the transformation is complete: in 1753, at the beginning of Davidson’s story, Voltaire was, in contemporary terms, like Michael Moore and Susan Sontag all mixed up: a provocateur who was also a universal literary celebrity. By the end, he was more like a cross between Andrei Sakharov and Mr. Toad of Toad Hall—a conceited grand bourgeois with a big house who was also one of the first dissidents, embodying a whole alternative set of values, and who came to be treated even by the government almost as an independent state within a state. How this came about, and without any Tolstoyan repentance or self-remaking, is one of the great stories of literary evolution.

Davidson tells it well, too. In 1753, Voltaire was in flight from Frederick the Great, of Prussia, who had taken him in as a kind of house philosopher at Potsdam. Voltaire may have imagined that he would rule hand in hand, philosopher and king, but soon discovered that he was there merely as an exotic intellectual toy. (“We shall squeeze the orange,” Frederick had said, secretly, “then, when we have swallowed the juice, we shall throw it away.”) Even after the falling-out with Frederick, Voltaire knew that he had some big guns on his side. The foreign minister of France, the Duke de Choiseul, was a fan, as was Mme. Pompadour, the King’s mistress, not to mention the Empress of Russia. He was also, luckily, very rich, in no small part because of his participation in a bizarre swindle devised by a mathematician friend, who, back in 1728, realized that the French government had authorized a lottery in which the prize was much greater than the collective cost of the tickets. He and Voltaire formed a syndicate, collected all the money, and became moneylenders to the great houses of Europe.

During his escape from Frederick, Voltaire first thought of going back to France, which he loved as only Frenchmen who have been away from it can. But a message from his old friend Mme. Pompadour confirmed the stunning news that the King had exiled him and forbidden him to return. (This turned out to be not quite true; the old man had probably said something merely pettish, like “Tell him to stay away!”) The terms of his exile were unclear, but Voltaire decided to move someplace close enough to feel like France and far enough away to keep him out of the official grip. He chose Geneva, which was then a small, suspicious Calvinist Protestant city-state. Through the good offices of a prominent Geneva friend, he found, and managed to rent, a small estate. He moved in with his new love, Mme. Denis, and renamed the villa Les Délices, the Delights. Although it was his later, sister retreat at Ferney that became legendary (he moved there in 1765, after a series of feuds with the Calvinist authorities in Geneva), it was his escape to Les Délices that marked a new epoch in his life.

Voltaire’s work, to this point, consisted essentially of a mass of journalism, essays, poems, potted, vivid histories, and historical plays all pulled together in the public imagination by a single strong personality. The “philosophy” that ran through it, though allergic to sectarian piety, was still officially Deist—partly because this was insurance against accusations of atheism, partly because, in a slightly condescending spirit, Voltaire was in favor of a benign, supervisory God in the way that British leftists used to be in favor of the Queen, or in the way that Yankee free agents are in favor of Joe Torre; it’s nice to think that someone genial is overseeing things. But there doesn’t seem to be any evidence that he actually believed, with any intensity or appetite, in “spiritual” experience, or found the sense of God’s presence even momentarily engaging. But then Voltaire was never exactly a “philosopher” in the conventional sense; his philosophy is almost always a moral instinct rendered as a dramatic gesture, rather than consecutive thoughts turned into a logical argument. As with Victor Hugo and Zola, his moral instincts were so good that we still intellectualize the dramatic gestures they became.