Like the instrument he mastered over six decades, Washington jazz bassist Keter Betts was elemental and essential, both to the sound of the city in which he had lived for more than 50 years and to those he played with -- whether over several decades as Ella Fitzgerald's most trusted and dependable accompanist or in the moments he graciously sat in with young talent at local jazz venues.

Betts, who died Saturday in his Silver Spring home at 77, seemed to be everywhere, perhaps due to a geniality and gregariousness that the years did nothing to diminish.

Betts's role in the jazz community, and the larger music community, reflected the traditional role and responsibility of the bass in a jazz ensemble: to anchor but also to provide a core pulse, to cushion and contextualize the sound of others but also to illuminate and inspire. As a player, Betts displayed impeccable taste, an insistent sense of swing, gorgeous tone and an appreciation for melody rooted in his collaborations with original song stylists such as Fitzgerald and Dinah Washington.

Little wonder, then, that Betts was one of the most sought-after bassists, and not only in a jazz context. In the early '90s, legendary R&B group the Orioles asked Betts to do a night's session work on an album and he ended up writing a set of arrangements, several days worth of work. When it came time to settle, Betts asked for a pittance. It was an act of generosity repeated time and again.

Betts taught and mentored generations of local jazz musicians and countless students he encountered in workshops and school programs, from elementary to college level. A teddy bear of man, with a perpetual smile, Betts preached the gospel of jazz, and the spirit of creativity, with grace, charm and enthusiasm, seeding future fans for a great, original American music form that, sadly, always needed great ambassadors. To hear Betts's wise discourses on jazz, his stories about the brilliant artists and improvisers he worked with, was to recognize the breadth of his own accomplishment.

Betts was probably best known for his long partnership with the grand First Lady of Song, Ella Fitzgerald, starting in the mid-'60s. Betts had spent years accompanying Washington, following a road apprenticeship with R&B saxophonist Earl Bostic and several years of seasoning on the club scene of the city he'd moved to in 1947, just a year out of high school.

But before hooking up with Fitzgerald, Betts would figure largely in one of the most significant musical movements of the '60s. In 1961, he and guitarist Charlie Byrd, already veterans of State Department-sponsored cultural goodwill tours of Europe and the Far East, were invited to Latin America. In Brazil, they discovered the simple yet beguiling and hypnotic sounds of bossa nova, which melded Brazil's infectious samba with West Coast-style cool jazz.

Betts was particularly enamored of the music and spearheaded a recording session at Pierce Hall in All Souls Church on 16th Street with Byrd and tenor saxophonist Stan Getz, who sensed that his rich, breathy vibrato would sound magnificent playing this new music. It was Getz's record date and Getz's label, Verve, but it's Betts's ebullient and ingratiating bass vamp that introduces the opening track, Antonio Carlos Jobim's "Desafinado," and sets the mood for 1962's "Jazz Samba," the jazz album that introduced and popularized bossa nova worldwide. Byrd and Getz always get the credit for that, but it was actually Betts who had the vision and inspiration, though he was forced out of Byrd's group soon after, just as the music exploded. Betts seldom talked about any disappointment over how history charted his contribution, but always took great pleasure when writers and fellow musicians recognized his significant role.

A few years later, Betts met Fitzgerald through Ray Brown -- one of his favorite partners on the golf courses they encountered on jazz tours around the world. Brown, himself one of the greatest of jazz bassists, had once been married to Fitzgerald and later managed her career; putting the singer and Betts together would be one of his greatest moves. From the start, they were simpatico, something particularly evident in concert during their showcase voice and bass duets -- daring dialogues and dances of rhythms and melodies that could be beautifully elegant one moment and wildly inventive the next.

Fitzgerald often told interviewers that Betts had a sixth sense as to what she needed, that it was his bass, not the drums, that drove the music. No one, she said, drove it better, and no one drove it as long, from 1964 until 1993, when Fitzgerald stopped touring because of declining health (she died three years later). But before that, there would be 50 European tours and an endless string of American concerts, including one at the Kennedy Center, during which Betts brokered a rare interview with the notoriously shy Fitzgerald for this reporter.

In the last few years, Keter Betts had his own serious health problems (he was diabetic much of his life), but he kept on playing with undiminished energy and imagination, kept on mentoring young musicians and gleefully challenging his peers. And he continued to embody the substance and spirit of the music he so loved. Jazz elevated Keter Betts to worldwide renown of his own and he in turn elevated everyone fortunate enough to be around him.

Keter Betts spent his life playing bass with energy and imagination.