Caldwell’s hit single, What You Won’t Do For Love, shot to the top 10 on Billboard Hot 100 in 1978 and broke barriers in the R&B genre.
Caldwell had been battling a long illness, his wife, Mary Caldwell, said. He was 71.
His songs have since been sampled across genres by artists ranging from Tupac Shakur and Common to Ella Mai.
He would later transition to song-writing, penning tunes for Neil Diamond and Roberta Flack.
Questlove led tributes to Caldwell on Instagram, lamenting the fact that he never got to meet Caldwell in person.
“Caldwell was the closing chapter in a generation in which record execs wanted to hide faces on album covers so perhaps maybe their artist could have a chance,” he wrote. “Man such a missed opportunity to meet a legend. Thank you for your voice and gift.”