After the couple split, around 1930, the enterprising and well-educated Ms. Armstrong formed her own successful big band. The group’s relatively short life span suggests why a musician like Ms. Armstrong had such a well-developed set of business skills. “She could get anyone in her group because she was so respected as a musician. But they didn’t really promote her as a bandleader, so her bands weren’t as successful as male bandleaders’,” said Courtney Bryan, a New Orleans-based pianist and scholar.

Ms. Armstrong eventually stepped away from music, working for years as a clothier, restaurateur and teacher, though she eventually returned to performing. In this way, her story reflects that of another eminent 20th-century pianist, Mary Lou Williams, whose compositions, arrangements, piano virtuosity, organizing and mentorship made her one of the most versatile — and crucial — figures in jazz history.

An early collaborator with Duke Ellington and Andy Kirk (who made her his lead arranger), Ms. Williams was slow to take off as a solo act; again, presenters felt disinclined to promote a strong female instrumentalist. In the eyes of musicians, though, she was nonpareil. In the 1940s, Ms. Williams offered her Harlem apartment as a crash pad and a jam-session hub, as well as a safe haven for fellow players. In the 1950s, distressed with the jazz world, she converted to Catholicism and temporarily retired from the stage. But even in absentia, she supported the music by founding the Bel Canto Foundation, which raised money for struggling musicians. She funded it by running a thrift store.

“It was about community,” said Woody Shaw III, the recently appointed executive director of the Mary Lou Williams Foundation, who is also Maxine Gordon’s son. “There was a natural sharing of information, and Williams found herself often in a kind of matriarchal position. These men were younger than she was, and needed guidance and intervention — whether it was through her creating her own businesses and organizations that specifically accommodated the needs of musicians, or allowing them to stay in her home when they were having difficulties.”

Through his work with the foundation and with his own company, Moontrane Media Group, Mr. Shaw has himself become a crusader for artists’ rights, helping musicians claim copyrights and royalties for their work. Today, with jazz’s constricting gender roles slowly eroding onstage as well as off, Mr. Shaw describes himself as an inheritor of a mantle worn by figures like Mary Lou Williams and Maxine Gordon.

Mr. Shaw called himself an “amalgamation of these influences and values, over the generations.” He added: “I’m trying to help legendary musicians move into the 21st century, in terms of how they brand and market their legacies and tell their stories. And then there’s the question of, how do we help musicians gain a level of control over their economic and artistic destiny in this generation, a control that they didn’t have in the past?”

For all her devotion to the musicians she advises, Ms. Gordon describes this work in unsentimental terms. “It was a career that I did because people would ask me to do things that I didn’t know how to do, and I’d just find out how,” she said. “There’s improvisation in the way we do business. If something came up, we had to figure it out.”