When they first met in the 1970s, they were two of the most famous entertainers on earth -- Michael Jackson and Paul McCartney.
They became good friends. Their partnership in the early 1980s produced hits like "Say Say Say" and "The Girl Is Mine."
"They're pure pop lovers with some of the greatest sense of melody," former editor in chief for Vibe and Spin magazines Alan Light told ABC News. "And students of old Hollywood films and early rock 'n' roll records, and lovers of cartoons. There was a lot of common ground between them."
But the relationship between Jackson and McCartney soured in 1985. That year, Jackson entered into a bidding war with McCartney for the rights to the Beatles song-copyright catalog. Jackson won, paying $47.5 million for more than 200 songs, including classics such as "Yesterday" and "Let It Be."
The details of the 10-month negotiations never became entirely clear.
"The story goes that one day at Paul McCartney's house they were having dinner and Paul casually mentioned that the way to make real money in the music business is through publishing," New York Times music reporter Ben Sisario told ABC News. "Michael took that to heart."
Alan Light said, "One thing that was speculated was that Michael kind of knew how much Paul was going to bid for this and knew what it was going to take to top that bid."
Although Jackson's financial affairs are now reportedly in disarray, Sisario said the acquisition of the songs was the move of a very smart businessman.
"Michael Jackson's investment in the Beatles' catalog was one of the most brilliant coups in all of music history," Sisario told ABC News. "He got his hands on the most valuable songs that there are for a pretty small amount of money. That has ballooned from about $50 million into more than a billion dollars."
But McCartney was furious, and the two reportedly didn't speak for years.
"You know what doesn't feel very good," McCartney said as recently as 2006, "is going on tour and paying to sing all my songs. Every time I sing 'Hey Jude,' I've got to pay someone."
"It's not just about the money," Sisario said. "It's about music. It's about what Paul McCartney created with John Lennon. I mean, this is his legacy to the world. And naturally he wants to own it, he wants to control it."
Since Jackson's death Thursday, McCartney has taken a much softer line. In a statement posted to his Web site this weekend, McCartney said, "I feel privileged to have hung out and worked with Michael. He was a massively talented boy man with a gentle soul."
Jackson's passing is raising new questions about what will happen to the Beatles catalog.
Earlier this year, some press reports suggested that Jackson, feeling badly about the rift with McCartney, had plans to leave Sir Paul the rights to the songs in his will.
Those reports are unconfirmed, and an army of lawyers is currently working to sort out Jackson's financial matters. At the time of his death, the pop icon was an estimated half-billion dollars in debt. Jackson's song collection was his largest asset.
There are conflicting reports about the executor of Jackson's will. One recent report says that Janet Jackson will be the executor of her brother's will; TMZ, the entertainment Web site, says Randy Jackson will take control of his brother's estate.
Alan Light too stressed that reports of Jackson leaving the Beatles' catalog to his old friend are, for now, just rumors.