The young Miller drew inspiration from seeing the supremely self-confident Ali on TV and started learning to defend himself. (The real Miller became an accomplished kick boxer and shared the ring briefly with Ali in an exhibition bout before focusing on a writing career.)
The two men met and developed a friendship, which the opera depicts in scenes that take place in the Louisville, Ky., home of Ali's mother. "Champ, you changed my life," Miller sings to Ali. "When I was a kid, you made me believe I could do anything."
Miller is a dual character in the piece, portrayed as a child by a boy soprano, by a baritone as an adult. Miller's parents and Ali's mother are also characters. And, of course, there's the "The Champ" himself.
" 'Mr. Champ,' as we call him," said Soloman Howard, the bass who will sing the role of Ali in the premiere. "It's an honor to portray someone you idolized growing up. But my first reaction when they asked me was: 'What? Ali? Me?' "
The D.C.-born Howard, 32, a member of the Domingo-Cafritz Young Artist Program, recently sang the role of Joe in several performances of the company's brilliant production of "Show Boat" last month.
He settled on a vocal career while studying at Morgan State University, where he sang in the school's celebrated choir, and earned a graduate degree at the Manhattan School of Music. But Howard brings more than the vocal chops to the role of Ali.
"I have an athletic background," the singer said. "I played football and did some sparring with my uncle in Baltimore. He would show me things from time to time, ways to take care of myself, 'just in case,' he would say."
Still, stepping into the operatic ring in the guise of one of the 20th century's most iconic men has to be a little intimidating, especially since Ali's own speaking voice is so well known.
"It's extraordinarily challenging," Howard said. "I was kind of shocked that the part calls for a bass. Ali has more of a tenor voice. But it was very musical to me. There was kind of, sort of a rhythm in which he spoke, with elongated phrases. Making him an operatic figure just made sense to me."
In addition to going against expectations when it came to the vocal range for the title character, Sparr avoided writing the opera in an all-out American style. He took inspiration from Eastern cultures, especially gongs and dharma drums.
"Davis told me it felt the air was electrified when Ali walked into a room," the composer said. "I wanted to create a shimmering sheen in the orchestra."
(The air would certainly become electrified if the 71-year-old Ali were to attend the premiere. That does not seem likely, but he and his family have been informed about the new opera.)
For Howard, the chance to be Ali, if only for an hour, is exhilarating.
"I feel I'm drawing something from him," Howard said. "He didn't always believe he was the greatest, but he would tell himself that. In later years, he had to psych himself out. I can relate to that. I often tell myself things for encouragement. The amount of charisma, charm and character he possesses is just amazing. To me, he's the friendly giant."
If you go
"Approaching Ali" will be performed at 7:30 p.m. Saturday and 2 p.m. June 2 at the Kennedy Center's Terrace Theatre. Tickets are $30. Call 800-444-1324 or go to kennedy-center.org.