Chris Jasper, a Juilliard-trained keyboardist, singer and songwriter who brought an expansive musical vocabulary to the long-running R&B group the Isley Brothers, helping push them into a new hit-making era in the 1970s and ’80s with singles like “That Lady” and “Fight the Power,” died on Feb. 23. He was 73.

His death was announced in a statement on his Facebook account, which noted that he had been diagnosed with cancer in December. The statement did not say where he died.

Mr. Jasper, who was also a producer, started his decade-long run as an official member of the Isley Brothers in 1973. He added musical complexity to the long-running R&B group as it took on a richer, funkier style for a new decade.

Looking back on the Isley Brothers’ sound in a 2020 interview with Rockin’ Hot Radio, a Delaware-based station, he said, “It’s R&B, of course,” but added that he borrowed “voicings that were used in classical music, and in particular the Romantic period, with composers like Debussy, even 20th-century composers like Gershwin.”

During his tenure, the group lodged more than a dozen singles on the Billboard Hot 100 and more than a dozen albums on the Billboard 200 — six of them in the Top 10, including “The Heat Is On,” which reached No. 1 in 1975.