Johnny Otis, an influential bandleader and a ubiquitous presence in rhythm-and-blues music who was credited with discovering singer Etta James and writing such hits as “Willie and the Hand Jive” and “Every Beat of My Heart,” the song that launched Gladys Knight, died Jan. 17 at his home in Altadena, Calif.

His manager, Terry Gould, confirmed the death but did not disclose the cause. Mr. Otis was 90 and widely promoted as the “godfather of rhythm and blues.”

At the dawn of the musical genre in the 1940s, Mr. Otis was an iconoclastic figure: a son of Greek immigrants who grew up in a black neighborhood in northern California and embraced African American culture during a period of strict racial segregation.

“As a kid, I decided that if our society dictated that one had to be black or white, I would be black,” he wrote in “Listen to the Lambs,” a 1968 book penned in reaction to the earlier Watts race riots in Los Angeles. The title was taken from a black spiritual and was a meditation on politics.

In a career spanning more than six decades, he was a drummer, vibraphonist, club owner, disc jockey, record label owner and talent scout. He first made an impression in show business as a bandleader, notably with his 1945 hit recording of Earle Hagen’s jazz standard “Harlem Nocturne.”

After further entries on the Billboard R&B charts, his 1958 recording of his own composition, “Willie and the Hand Jive,” sold more than 1 million copies; it was later covered by guitarist Eric Clapton. Another Otis composition, “Every Beat of My Heart” became a best-selling record in 1961 for Gladys Knight and the Pips.

The Otis band, with Mr. Otis on drums, backed Big Mama Thornton on her original version of “Hound Dog” (1952), later a signature song for Elvis Presley.

In 1994, Mr. Otis was inducted into the Rock and Roll Hall of Fame. “Over the years he has exhibited an uncanny ear for talent, and by bringing that talent to the fore has served to advance the growth and development of rhythm & blues,” his citation read.

Johnny Alexander Veliotes was born Dec. 28, 1921, in Vallejo, Calif. Survivors include his wife of 70 years, the former Phyllis Walker; and seven children. His son, Shuggie, played guitar in the Otis band and recorded several albums under his own name.

Mr. Otis began his career at 18 drumming with a juke joint pianist near his home. In his 20s, he went to Los Angeles to drum with Harlan Leonard’s Kansas City Rockets, a popular draw on Central Avenue, the city’s black entertainment strip, and recorded with jazz saxophonist Lester Young. When a chain saw accident impaired his right hand and limited his drumming, Mr. Otis took up vibraphone.

In part because it was too expensive to support a large band, Mr. Otis started a “jump combo” in the late 1940s. This group, usually with fewer than 10 musicians, focused on the blues and boogie-woogie.

“To compensate for all the instruments we were eliminating, we had to put in some new ones, each with a fuller sound: an electric guitar, a blues guitar, a boogie piano,” Mr. Otis told the Los Angeles Times. “We ended up creating a new hybrid music that became known as rhythm and blues.”

By the next decade, the band had evolved into the Rhythm’n’ Blues Caravan, a touring revue. Several of its singers were discovered at talent shows sponsored by Mr. Otis’s Barrelhouse Club in Watts. Performers discovered at the Barrelhouse included Etta James; jazz vocalist Esther Phillips, who first recorded with Mr. Otis as a 13-year-old blues singer; Little Esther; and the vocal group the Robins, which evolved into the Coasters.

“Johnny heard something in people and could nurture it and make them stars,” said George Lipsitz, a black studies scholar and co-author of Mr. Otis’ 2010 memoir “Midnight at the Barrelhouse.” “For example, Etta James and Esther Phillips came to him as a teenagers. Not everybody could discover people, not everybody could push them forward.”

Mr. Otis’s talent-scout activities were not limited to his own ensemble. At a talent show he judged in Detroit, he heard Jackie Wilson, Little Willie John and Hank Ballard (later of the Midnighters). Mr. Otis couldn’t decide on a clear winner but introduced all three to the King record label.

One singer who didn’t impress him was Sonny Bono, who auditioned for Mr. Otis’s Dig record label in the mid-1950s.“He had absolutely no talent. He couldn’t sing, couldn’t dance, had no personality,” Mr. Otis told the Santa Rosa Press Democrat in 1998. “But I liked him because he made it anyway.”

Mr. Otis enjoyed a prolific career beyond show business, partly because the rise of rock-and-roll had sidelined his musical style. He became a painter, sculpture, pigeon breeder, organic farmer, minister and community activist. In the 1960s, he wrote editorials for the Sentinel, an African American newspaper in Los Angeles. One piece he wrote about housing discrimination led to a cross burning on his lawn, said Lipsitz.

In the late 1960s and 1970s, Mr. Otis worked for Mervyn Dymally, a Democrat then in the California state assembly and who later became a U.S. congressman. For a time, Mr. Otis owned a grocery store and marketed Johnny Otis Apple Juice.

In later years, Mr. Otis sometimes spoke humbly about his own musicianship, viewing his rhythm-and-blues career from a jazz perspective.

“Some so-called jazz musicians, the bush leaguers, would consider people like Sonny Thompson, Roy Milton or myself, who came out of big band swing jazz, as traitors to the jazz cause,” he told New York Rocker magazine in 1982. “I might take that seriously if I were a great instrumentalist and a man who created deathless art, but I never was. I was kind of a nice drummer and later I dinged on the vibes and boogies three-finger style on the piano.”