In the early, bitter post-Beatles years, a pro-Lennon/anti-McCartney prejudice was common among rock journalists, who generally saw Lennon as an edgy, charismatic genius and McCartney as a bland, pretty egomaniac who, in Lennon`s words, was writing "granny music." But Norman`s assertion that McCartney was a bit player in the Beatles seemed extreme.

Norman now says he retreated from that position some years ago while writing his 2008 biography of Lennon, John Lennon: The Life. During his research for that book, he had a relatively affable telephone conversation with McCartney, who had called Norman without prior warning, wanting "to see what this fellow who seems to hate me so much is like." McCartney then agreed to answer several queries by email about the early Beatles days.

In 2013, Norman emailed McCartney, saying he would like to write his biography as a companion to the Lennon book. He did not expect McCartney to collaborate with him, but he did ask for tacit approval so he could talk to the ex-Beatle`s friends and associates. (Norman has written books on other living rock stars, including Elton John and Mick Jagger, but has never based a biography on direct access to any of his subjects, relying instead on the memories of others.) "Within a fortnight, I had a four-line email thanking me for my letter, saying he was happy to give "tacit approval" and wishing me all the best. Given what had gone before, it was magnanimous of him," Norman tells me over lunch at a London restaurant.

Norman, who has met McCartney only twice-both were brief encounters-says he had badly misjudged him when writing Shout! and that as he progressed with his research, he found he was "unprepared for the amount there is to admire-as well as his complexity and insecurity."

Norman`s new book is his seventh rock biography (he is also a novelist, poet and playwright). In the early 1970s, he became the first pop music critic at The Times of London; when Times Newspapers ceased publishing for a year following an industrial dispute in 1978, Norman decided to use the downtime to write a book about the Beatles. Shout! was published more than a decade after Hunter Davies`s authorised biography of the Beatles (The Beatles), so Norman thought people would be ready for a second major biography of the world`s most successful rock band. Lennon`s murder the year before Shout! was published likely generated more demand for the book, which has sold more than 1 million copies.

His McCartney biography is a compelling narrative about a working-class Liverpudlian whose extraordinary musical gifts made him the most successful songwriter in history. Norman says what surprised him most about his subject was that McCartney has always been, and remains, insecure: "It`s like George Orwell says, "Every life from the inside seems like a record of failure," and McCartney still feels a desperate need to prove himself." In 2015, McCartney told the British edition of Esquire, "All my life I`ve been trying to win a school prize or trying to do OK in an exam or trying to get a good job, something where people go: You`re good."

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McCartney`s extended family-his stepmother Angie, stepsister Ruth, cousin Ian Harris and brother Michael-was an important source for Norman as he researched McCartney`s early years. The author says McCartney`s father, Jim, is essential to understanding the ex-Beatle, because he not only implanted in his son a love of traditional jazz-he played trumpet and piano, and for years led Jim Mac`s Jazz Band-but also instilled in the McCartney boys values they would retain throughout their lives. An early example is when McCartney found a pound note, which was a lot of money in the years right after World War II, outside his Liverpool home. His father insisted he hand it in to the local police station.

"Paul still has these basically decent values," Norman says.

That decency extended even to the Beatles hardcore female fans (nicknamed Apple Scruffs by George Harrison) who hung around outside the entrance of McCartney`s St. John`s Wood home for years. McCartney maintained a convivial relationship with the young women, even when they followed him to his weekend home in East Sussex. Peter Cox, who worked with McCartney`s first wife, Linda, on her vegetarian cookbook, told Norman, "Fans of Paul`s, especially Japanese ones, were continually turning up in the district, then getting hopelessly lost. [McCartney`s] Land Rover would gather them up, take them to the station and put them on the right train back to London."

Another important source was John Eastman, McCartney`s brother-in-law and lawyer, who revealed a great deal about the breakup of the Beatles, when McCartney was marginalised by his former band mates. "It really was Paul, Linda and John Eastman up against the might of the Apple lawyers and lawyers representing Allen Klein, the American businessman representing the other three Beatles," says Norman. "A minority up against corporate might."

Shortly before the beginning of the legal battle that would finally dissolve the partnership, McCartney became depressed about his decision to leave the group. In self-imposed exile in Scotland, Norman writes, "he began to chain-smoke, both legal and illegal cigarettes, and turned to whisky-his father`s favourite tipple-reaching for the bottle as soon as he awoke."

Although at the time the public perception was that the split was irreparable, behind the scenes, as Norman reveals, both Lennon and McCartney were deeply pained by their separation. Lennon told his second wife, Yoko Ono, that no one had ever hurt him the way McCartney had. Still, the two old friends began seeing each other again in 1972, after McCartney initiated a meeting in New York, where the Lennons were living.

By 1975, the rift had healed to the extent that the two had dinner together with their wives at Elaine`s-a now-closed favourite restaurant of New York celebrities-after which they retreated to Lennon and Ono`s apartment on Manhattan`s Upper West Side to watch Saturday Night Live. For all the public disputes and vitriolic exchanges as the Beatles disintegrated, the friendship forged in Liverpool during their teen years had survived. "They always had a tingling awareness of one another," Norman says.

Norman also writes movingly of McCartney`s grief at Lennon`s death and that of Linda, who died of cancer in 1998. Her death left McCartney, according to Norman, in a vulnerable state. And it led to what was probably one of the sourest notes in a life that has lacked much of the tabloid attention that many of his rock-god contemporaries have attracted: his brief marriage to Heather Mills, whom he met just a month after performing at the Linda McCartney tribute concert at London`s Albert Hall on April 10, 1999.

Many of McCartney`s friends couldn`t understand what drew him to a woman they believed was deceitful. It seemed that McCartney soon came to that conclusion himself. The couple divorced in 2008. In his final ruling, the judge in the case referred to McCartney`s amended petition that alleged "throughout the marriage the wife had shown a consistent inability to tell the truth." The judge, Hugh Bennett, seems to have supported McCartney`s claim. In the judgement, he wrote, "I am driven to the conclusion that much of her evidence, both written and oral, was not just inconsistent and inaccurate but also less than candid."

The most compelling explanation for why McCartney fell for Mills, who lost much of her left leg in an accident in 1993, came from another of Norman`s sources, Joe Flannery, a longtime friend of McCartney`s who had been the boyfriend of the Beatles` first manager, Brian Epstein. According to Norman, when Flannery asked McCartney why he was drawn to Mills, McCartney replied, "I looked at her leg and went, ‘A-ah.’"

Depending on how you read it, that quote-if accurate-is self-serving and patronising, or generous and endearing. It`s perhaps both. Norman`s book reveals those contradictions, and McCartney emerges from it as a textured but decent man. As Norman says, "If you have been worshipped every day of your life since you were 19 and haven`t turned into a monster, that`s pretty extraordinary."