A simple knock on the door of Muhammad Ali's "block-long" Winnebago a quarter century ago set off a chain of events that culminate this weekend with an opera based on the life of the man who knocked on the door and what happened after the most famous boxer of all time opened it.

The noted writer Davis Miller will see the most intimate moments of his life as a child and later as an adult unfold on stage Saturday night when the world premier of Approaching Ali opens at the Kennedy Center in Washington D.C. The initial run of the hour-long opera will be limited to two performances, on Saturday night and Sunday afternoon. Tickets are available.

The opera is based on Miller's book, The Tao of Muhammad Ali, which describes the numerous ways Ali influenced the North Carolina native and, as Miller explains it, "twice transformed my life."

The opera was spawned from another chance meeting between Miller and musician-composer D.J. Sparr (yes, the real name of the brains behind the opera's music) a few years ago in Richmond, Va.

When Miller found out what Sparr did for a living, he told the composer he thought a musical piece could be written about his book and the things Ali had done in his life, not only in boxing, but in his global humanitarian efforts and his wisdom. Miller urged Sparr to read the book, which he did. He was sold.

"When the Washington National Opera called me to come up with an idea, I had read Davis' book that summer, so I thought the topic about Ali and the setting of the intimate book Davis wrote fit really well with an American topic that our American opera would be interested in," Sparr told USA TODAY Sports this week during a phone interview. "Presenting Ali sort of as a Buddha figure, where kind of just being in the room with him changes things."

Being in the room with Ali, which Miller describes as "electrifying the air," certainly changed Miller's life, almost instantaneously, he says. The end of Ali's career marked the beginning of Davis' career as a writer.

Miller, now 60, was a 30-something, soon-to-be-unemployed video store manager in Louisville when he drove by Ali's mother's house and saw the Winnebago parked out front with license plates that read "The Greatest."

"I worked up the courage and knocked on the door," Miller says. "Ali invited me in, and did magic tricks for me.

"I told him he saved my life as a kid."

This was actually Miller's second meeting with his boyhood idol. By the time he was in college, he had already been greatly influenced by the heavyweight champion.

"First when I was a 10-year-old and my mother had died and I saw him on TV before the (Sonny) Liston fight," Miller says. "I felt like the glory train had passed through me."

As a child he suffered severe depression, which he later traced to being worried that his parents were going to divorce. "I prayed when I went to bed every night that they wouldn't get divorced," he says, and saw his mother's early death as the answer to his prayers. He later blamed himself for her death.

"I had been in and out of the hospital at that time because I was refusing to eat or even take fluids," Miller says. "I was in tough shape and I stayed in tough shape.

"At 16, I was 4-foot-10 and weighed 63 pounds, trying to basically remain 10 years old and live vicariously through Ali. Later I got motivated and tried to become a professional kick-boxer because of Ali, because there was no boxing in Winston-Salem, where I grew up."

During college in 1975, an acquaintance who happened to be the nephew of Ali's trainer, Angelo Dundee, told Miller that if he wanted to spar with Ali he should go to the fighter's training camp in Deer Lake, Pa.Ali sparred with anyone who showed up as he trained for his second fight with Joe Bugner, Miller was told.

So he did, and wrote about his experience in a piece for Sports Illustrated, for which he was paid the then-princely sum of $750.

"I promptly quit school, thought I was going to write a novel in six months and go on the Tonight Show," Miller says. "I had no clue. It didn't work that way."

It was that piece which he showed Ali in the Winnebago a dozen or so years later.

"I had the story and read it aloud to him, and he laughed at the appropriate times and didn't seem bored," Miller says. "He was fairly deeply Parkinsonian at the time and we play-boxed in his mom's front yard, and his mom invited me in for dinner. It felt like a seminal experience for me."

Miller immediatly wrote a long piece for Esquire magazine called My Dinner with Ali.

"Within a few weeks of that story being published it won several awards, and I was offered a gig as a boxing writer for Sport magazine," he says. "About half of the opera is based on that story, and the other half is based on my early life and seeing Ali on a television screen and getting inspired."

Miller says he knew "zilch" about opera coming into this project, and to this day has never seen one.

"I managed to torture out a couple of pretty good tunes and a general story, and then was shown my inadequacies by a premier librettist (one who writes the text of an opera) in the opera world, (Pulitzer Prize winner) Mark Campbell," Miller says. "He took the outline I gave him and those two tunes and fashioned it into a complete libretto.

"I don't think there's anything quite like this opera. I'm the protagonist in it, and it's me in my mid-30s on the tough brink of middle age, when I was struggling with stuff, and then the 10-12-year-old me after my mother had died. Ali and his mom, (Odessa Clay) are the second main characters.

"They picked out a person to be me (David Kravitz) who looks like me in my early 30s, and Solomon Howard, who's Ali."

One of Ali's great attributes was his ability during his career to spew out memorable lines such as "float like a butterfly, sting like a bee."

Miller and Campbell worked in several.

"There's a trio of men, bass and baritone," says Sparr, "and boy, they get going with 'your hands can't hit what your eyes can't see, your hands can't hit what your eyes can't see.'

"Then they say, 'Rumble, young man, rumble,' referring to Davis as a young boy trying to overcome his problems.

"It's about the moment in time where Ali influenced Davis. There's a part in the opera where it says, "What if he's brain dead, what if he's ill, what if he's in a wheelchair?" like the papers described him, and one of the things Davis' book describes is that Ali really wasn't like that at all."

For Sparr, 37, from Richmond, it's his first crack at opera — a one-hour opera takes about a year to put together, he says — and he's excited by the possibilities.

"It's really a privilege to write an opera because an opera costs many hundreds of thousands of dollars," he says, adding that a team of 60 people worked on Approaching Ali. "So it's not the usual thing for a composer to do. It's a once-in a lifetime kind of thing."

Miller is not quite ready to publicly watch his life laid bare before his eyes.

"I'm embarrassed by the whole thing," he says. "It's so personal. It's almost like walking around with my underwear on my head. I've heard the piano scores and the persons learning their lines. There was a moment in there where my dad has a really nice aria (an operatic solo), and I've heard it three times and couldn't stop crying.

"I'm not really comfortable being around it. I think it's going to be good. Maybe even uncommonly good. But it's tough for me to watch.

"My wife wants to see it, and even if Ali will not be there, I know some of his daughters will be. So I'm going to squirrel myself into a closet until it's over."

Ali and his wife Lonnie are enthusiastic about the opera, miller says. "They told me they want to do everything they can to support it.

"I'd be shocked if he (came to the premier). But they want to do performances of it at the Ali Center in Louisville and with the Kentucky Center for the Arts."

Miller even talks about performing the opera at Ali's home in Phoenix. "There's six singers or actors, and 10 musicians. So it's very intimate," he says.

Having become close friends over the years with Ali and his wife, Miller says the belief that "The Greatest" can no longer talk is simply untrue.

"He talks when he trusts you," he says. "He talks to his family, he talks to his friends. But since 1986 or '87, he's not talked much in public. Every once in a while, he will step out.

"He did have vocal cord surgery about two months ago. I have not talked with him since then, but Jamillah (one of his twin daughters) says he's talking the best he has in decades."

So what can people expect to take away from Approaching Ali?

"The opera is about loss and redemption, and it's also about how we have a tendency as a species to be sociopathic about people who have an illness," Miller says. "One thing I've learned about Ali is that he's still Ali. When I was spending time with him in the '90s, he was no less Ali than ever. In some ways his illness had made him obviously wise.

"As writers, we meet so many people, and you have friends and acquaintances and co-workers who all met the people they idolized, and invariably they're disappointed.

"Ali does not disappoint. He is absolutely as large as I hoped he would be."