On the 25th anniversary John Lennon's death, Spitz appeared on The Early Show to talk with co-anchor Harry Smith about some of what he learned during more than eight years of research.
A crucial part of "The Beatles: The Biography" is its insight into the creative partnership of Lennon and Paul McCartney.
"The Beatles: The Biography" describes Lennon's early years in Liverpool. His father abandoned Lennon's family when he was five, and his mother sent him to live with her sister, Mimi. His mother, Julia, was killed in an accident when he was 17.
"He felt like he never had anyone to nurture him, to discipline him," Spitz said. "His Aunt Mimi was a great disciplinarian, but also his great pal. John searched his whole life for someone who would be his role model. His best friend, (early Beatles member) Stewart Sutcliffe, died early, and it confused him further. When he found Paul McCartney, he found someone who was his mirror image."
The young McCartney also had suffered tragedy when his mother died when he was 14.
"It brought them together, yet they had a complicated relationship," said Spitz. "They threw sparks their entire relationship. It was really fascinating as well because they were both driven toward the same thing but away from the same thing as well."
From their earliest days, says Spitz, they had a different vision of what the band would become.
"Paul wanted (the band) to be the loveable moptops," he said, "and John wanted to be something darker and edgier, like The Rolling Stones. So they never resolved that. That's one of the things that broke up The Beatles."
Paul had joined "John's band," but soon he began controlling the music and the image.
"It had begun as John's band when he was 14 years old, and pretty soon it wasn't his band anymore, and I think he resented that," Spitz said.
John Lennon was, after all, a complicated character — both a peace activist and an angry man.
"I had discovered Paul's first girlfriend, who told me John once confided he never had a peaceful day in his life," said Spitz. "He drank when he was younger, discovered drugs in his early 20s, and rode them all the way through to the very end. He had a lot of demons and a lot of turmoil."
A question that has dogged every Beatles biographer and fan over the years is whether it was Yoko Ono and her relationship with Lennon which broke up The Beatles. Spitz sees a complex picture.
"Yoko was there to help John extricate himself from the group," he said. "He had gotten to the point he couldn't stand up to Paul McCartney anymore. His (first) wife, Cynthia, didn't really have the backbone. When he met Yoko, he found someone very strong who wasn't intimidated by Paul and had no regard for The Beatles."
Yoko was soon sitting in on the recording sessions, making comments and asking questions. The other Beatles, stunned, didn't know what to do about her.
"But John contrived to do that, and knew exactly what it was going to do," Spitz said.
Soon after, The Beatles announced their breakup. Contradictory rumors swirled for years, including one that the band members had been feuding ever since "Sergeant Pepper's Lonely Heart Club Band" was recorded. And always, there were rumors that The Beatles were considering getting back together.
Spitz believes that was never considered.
"The Beatles weren't sentimental about their image at all, but did protect it," he said. "They knew what they had done, and knew what their legacy was. I think they were resolved never ever to tread on that legacy. I don't think you would have seen them on the same stage as The Beatles again."
Spitz said that John Lennon was beginning to make peace with Paul McCartney, and with himself, when his life ended in violence at the age of 40.
"He was on the right track, which makes his death so much more tragic," said Spitz.
Was Lennon a musical icon? The hippie saint? The peace activist?
"All of that," said Spitz, although he is convinced Lennon would have detested the saint label. "He left us with the most incredible song book from the 1960s and the 20th century. That was a fantastic legacy."