For decades, most of what jazz scholars have known about the late, Philadelphia-based pianist and composer Hasaan Ibn Ali came from a single 1965 album – The Max Roach Trio Featuring the Legendary Hasaan.

That recording didn't exactly establish the idiosyncratic musician as part of jazz's new vanguard, but it did gather enough attention to prompt Atlantic Records to try a follow up – and that second recording, made in the late summer of 1965, has been the stuff of rumor ever since. Long thought to be lost, this album, entitled Metaphysics, was discovered in 2017 and has just, finally, been released.

When Hasaan Ibn Ali made his debut on Atlantic Records, he was 33 years old and living with his parents in Philadelphia. He rarely performed in public, more of a "phantom" than a legend, but within the community of musicians on the East Coast there was a steady hum of grapevine talk about the socially awkward pianist from Philly who could create Thelonious Monk-style whiplash one minute, and sprint up and down the keyboard like Art Tatum the next.

In Philadelphia, Ali was known for showing up at jam sessions, sitting down on the piano bench next to whoever was playing, and gradually taking over. Young musicians respected him, and feared him too: Saxophone legend Archie Shepp, who learned to play at those sessions, recalls Ali as an "imposing figure," saying that when the pianist started to play, he and other younger musicians would flee the bandstand to listen to his intense, questioning music.

Only one horn player could keep up with Ali – saxophonist Odean Pope, who made his recording debut on Metaphysics at age 26. Pope played and studied with Ali for years; he recalls visiting the pianist's house with his friend John Coltrane, absorbing ideas about jazz harmony that were galaxies away from typical bebop. The Metaphysics track "Atlantic Ones" shows that connection: Not only does it bear some similarity to the harmonic motion of Coltrane's iconic "Giant Steps," but it shows Ali and Pope engaged in an animated, rapidly evolving musical conversation.

For the second album, Ali wrote material for a quartet featuring Pope, and convinced Atlantic he needed several rehearsals ahead of the session – an unusual request at a time when many jazz records were made in a day, with no preparation. Despite an imperfectly tuned piano, the recording sessions were considered a success.

But weeks later, Ali was arrested for narcotics possession. That prompted label executives to shelve the project, sending Ali on a downward spiral: Within a few years, he stopped playing in public, and died in a convalescent home in 1981. By then, the Metaphysics master tapes had been lost in a vault fire, along with legendary recordings by Aretha Franklin, Ornette Coleman and other Atlantic artists. Assorted efforts by jazz historians to locate any recordings under Ali's name were fruitless – until 2017, when a monoaural "safety" backup containing most of the music of Metaphysics was found.

The release of Metaphysics roughly doubles Hasaan Ibn Ali's known recorded output. It won't reorder anyone's jazz cosmology, but offers insight about his music that confirms the recollections of many who heard and played with him. Brilliant and sometimes sloppy, it's loaded with musical provocations in the form of diabolical solo leaps and jagged, asymmetrical compositional ideas he likely would have developed further on future projects. Ali might have been hailed/tagged as "legendary" on his very first record, but as this vault discovery shows, he was really just getting started.