In 1971, Duane Allman swerved his motorcycle to avoid rear-ending a flatbed truck in Macon, Ga., and was fatally injured—leaving behind a 2-year-old daughter. Today, that daughter, Galadrielle Allman, 43, is co-producer of "Skydog: The Duane Allman Retrospective"—a seven-CD set due Tuesday from Rounder. The box is as much a musical biography as it is a daughter's attempt to understand a father she never knew.

"This project turned out to be a more complicated story than I expected when I started 13 years ago," said Ms. Allman from her home in Berkeley, Calif. "My dad wasn't some phenomenon who came out of nowhere. This box really documents a hard-working and earnest session musician who was searching for a new sound while he earned a living."

Duane Allman John Gellman

Duane Allman, of course, is best known today as the guitarist who founded the Allman Brothers Band in 1969 with his younger brother Gregg on lead vocal, guitar and keyboards. Before his death at age 24, Allman's vision launched a new country-blues style that showcased extended improvised solos and sparked the Southern rock movement.

"When Duane asked me to join his band in '69, he told me he was tired of being a studio robot." said Gregg Allman, who at 65 continues to lead and tour with the band today. "He played all those sessions as a steppingstone to where he wound up."

The new 129-track boxed set ($119) opens with recordings by the Escorts—the Allmans' first band in 1965, with Beatles and Yardbirds ambitions. In '66, the brothers reconfigured as the Allman Joys, and a year later they signed with Liberty Records and moved to Los Angeles. There, they became the Hour Glass—recording folk-rock and blue-eyed soul for the pop label. (Nine Hour Glass tracks appear on the set.)

"We hated that," Mr. Allman said. "That was me learning to write. Duane and I met a lot of great people out there, but the music we had to record for Liberty was way too processed. It wasn't us."

RAMBLIN' MEN From left, the Allman Brothers Band in 1969: Dickey Betts, Duane and Gregg, Jaimoe Johanson, Berry Oakley, Butch Trucks Redferns/Getty Images

Frustrated, the brothers returned home to Daytona Beach, Fla., in 1968—forming the 31st of February, which resulted in Gregg Allman's midtempo classic "Melissa." "Unfortunately, our Liberty producer didn't want us to leave," said Mr. Allman. "He agreed to let Duane and everyone else in the band go if I returned to finish the contract. I had no choice, so I went back."

Alone, Duane quickly made a name for himself as an in-demand slide and lead guitarist. He appeared on recordings by Clarence Carter, Wilson Pickett, Aretha Franklin, Boz Scaggs, King Curtis, Lulu, Laura Nyro, Herbie Mann and many others. His nickname—Skydog—was inspired by how his long hair fell and by Pickett's appreciation of his birdlike guitar sound.

On the new set, Allman's signature twang evolves rapidly from rural flavoring (Franklin's "It Ain't Fair") to dominant blues ingredient ( Ronnie Hawkins's "Sick and Tired"). Allman's lucrative session work continued until the release in '71 of the Allman Brothers' transforming album: "At Fillmore East."

Along the way, Allman appeared on Eric Clapton's "Layla" in 1970—and was invited to join Mr. Clapton's Dominos: "He wrote my mother a letter about how excited he was by the prospect and how it could mean a better life for us," said Ms. Allman. "But his connection to his band and the creative freedom he had ultimately were obstacles."

Gregg Allman was at the "Layla" session. "Duane just went into the studio and turned that thing around," he said. "He played a little more guitar than Eric that day, but it was loving competition."

What does Ms. Allman think about her father now? "I think assembling all of his material would definitely have moved him. I think he'd be immensely proud."