In the spring of 1989, the Daily Telegraph sent Alexander Boris de Pfeffel Johnson to Brussels to cover what was then the European Economic Community. Johnson, who was twenty-four, knew the city well. His father, Stanley, had been one of the first British bureaucrats appointed to work at the European Commission after the United Kingdom joined the bloc, in 1973. Johnson, his parents, and his three younger siblings moved to Belgium when he was nine years old, joining a sleepy community of expats. Johnson was a clever boy. He learned to speak French without an accent.

When Johnson returned, his father invited an experienced Brussels correspondent, Geoff Meade, to lunch at the family’s large house near Waterloo. Meade and his wife, Sandra, were having drinks when a taxi pulled up. “We hadn’t been led to expect anyone else so it was a surprise to see this outstandingly blond chap jump out in the loudest pair of Bermuda shorts possible. I’ll never forget it,” Meade recounted in “Just Boris: A Tale of Blond Ambition,” Sonia Purnell’s haunting biography, from 2011, of the man expected to be Britain’s next Prime Minister. “But it became clear over lunch that I had been invited there as the established hand to meet and help Boris.”

Purnell served as Johnson’s deputy in the Telegraph’s Brussels bureau, and her portrait of the politician as a young reporter makes an indelible impression. At first, Johnson was lost. He had been fired from his first job in journalism, at the Times of London, for making up a quote about Edward II’s relations with a boy, which he had attributed to his godfather, an Oxford don. Johnson was disorganized and had few reporting skills. But he had a knack for comedy and a genius for spotting a counter-narrative. In a collection of his journalism, “Lend Me Your Ears” (2003), Johnson describes a free-market approach to trying out opinions: “There will always be someone ready to buck the conventional wisdom, ready to buy when the market is low.” Johnson realized that conventional British reporting on the procedures of the E.E.C. (which was renamed the European Union in 1993) was reverential, accurate, and dull. He went the other way.

Six months after he arrived in Brussels, Johnson began to churn out sly, exaggerated stories that cast the European project as bureaucratically insane. Snails were to be designated as fish, he wrote. Berlaymont, the European Commission’s headquarters, was to be blown up. Condom sizes were to be standardized. “The E.C. has dismissed Italian plans for a maximum condom width of fifty-four millimetres,” Johnson reported in the Telegraph on May 8, 1991. “M Willy Helin, spokesman for the commission’s industrial standards division, said: ‘This is a very serious business.’ ”

Johnson’s stories caused a sensation. His British rivals were ordered to find and replicate them, which they failed to do, because there was rarely anything there. He was a figure, almost, of self-parody. He drove a battered red sports car. His clothes had holes in them. He turned up late at press conferences and spoke deliberately bad French. European officials had no idea what to do with him. “We answer his attacks,” one said. “But the problem is that our answers are not funny.” On one occasion, as Johnson made yet another grand, dishevelled appearance at a news briefing, a French reporter asked, “Qui est ce monstre?” Johnson rapidly became a darling of the Conservative Party’s Euroskeptic right, and a favorite of Margaret Thatcher’s. “Everything I wrote from Brussels I found was sort of chucking these rocks over the garden wall and I listened to this amazing crash from the greenhouse next door over in England,” Johnson told the BBC’s “Desert Island Discs,” in 2005. “It really gave me this, I suppose, rather weird sense of power.”

It is hard not to discern a psychological motive in Johnson’s assault on the E.U. machine. As his siblings have pointed out, Brussels had been a deeply unhappy place for him as a child. The Johnsons had lived in a big house in the suburbs, next to a forest. According to Purnell, Rachel Johnson, Boris’s younger sister and also a prominent journalist, has compared life at the time to “The Ice Storm,” the Rick Moody novel about a disintegrating family. “There was the same bleakness, the disconnection,” she has said. Stanley had affairs, and the marriage slowly fell apart. When Johnson was ten, his mother, Charlotte, suffered a breakdown and was hospitalized for nine months. Boris and Rachel were sent to boarding school. When Johnson came back to Brussels, he had a wife, Allegra Mostyn-Owen, whom he had met at Oxford. The couple lived in an unprepossessing apartment above a dentist named Goris. Johnson disappeared into his work at the Telegraph. “I used to get the paper—yesterday’s news—and there’s his byline in fucking Zagreb,” Mostyn-Owen later recalled. “You get past caring and you start drinking malt whisky.” Mostyn-Owen feared that she would crack up, as Johnson’s mother had. (The couple divorced in 1992; Johnson married his second wife, Marina Wheeler, whom he had known as a child in Brussels, twelve days later.) In the Telegraph’s offices, which overlooked an elegant square, Johnson would lock his door and shout obscenities to himself, while he worked himself up to write each story. “This bizarre ritual, to those who witnessed it, was an insight into the torrent of focus and drive that lies beneath Boris’s affable exterior,” Purnell writes.

In 1994, Johnson was recalled to become the Telegraph’s chief political columnist. He was a newspaper star. But his reporting was no longer credible. “He was by then a caricature, and he had to go,” James Landale, then a reporter at the Times of London, who is now the BBC’s diplomatic correspondent, told Purnell. To mark Johnson’s departure from Brussels, Landale wrote a poem, based on Hilaire Belloc’s “Matilda,” in which “Boris told such dreadful lies / It made one gasp and stretch one’s eyes.” When Johnson returned to London, he confessed to an editorial writer at the Telegraph that he had no political opinions. “You must have some,” the colleague reassured him. “Well, I’m against Europe and against capital punishment,” Johnson said. “I’m sure you’ll make something out of that,” came the reply.

To the British public, Johnson is an immediately recognizable figure in the culture. He is Bertie Wooster. His hair is a mess. He falls into ponds. You can find yourself feeling sympathetic toward him, because of an intimation of vulnerability and a sense that he is fundamentally unserious. “Boris has the capacity to lose his way in a sentence, like a child in a nativity play. You want him to succeed, and when he does you share in his triumph,” Michael Gove, Johnson’s old friend from Oxford, fellow-Brexiteer, and political rival, has said. In “Boris: The Adventures of Boris Johnson,” Andrew Gimson, a former colleague of Johnson’s, describes his ability—which is almost unique among contemporary British politicians—to cheer people up. “While many politicians have the urge to perfect society, Boris believes in the imperfectability of mankind, and especially of himself,” Gimson writes. (The biography was published in 2006 and updated in 2016.) “He does not seek to attain impossibly high standards, nor does he impose them on others.”