Billy Paul, the singer, who has died aged 81, was best known for Me and Mrs Jones (1972), the sultry and heart-rending "Philadelphia Soul" love song which describes the pangs of a man having an extra-marital affair with a married woman; the track was Paul's only No 1, but his achingly smooth and faintly lisping rendition has endured for decades.
He was born Paul Williams in North Philadelphia, Pennsylvania, in 1934. His childhood was steeped in music and his naturally high voice and adaptable vocal range meant that he had a particular affinity for female soul and jazz singers. "They just did more with their voices," he later explained, "and that's why I paid more attention to them."
Educated at the West Philadelphia Music School and the Granoff School of Music, by the time Paul was 16 he was performing at the ritzy West Philadelphia jazz hotspot Club Harlem, where he appeared on the same bill as Charlie Parker, a year before Parker's death.
After changing his name to Billy Paul, he was soon being booked for regular club appearances and concert performances on the Philadelphia music scene.
In 1952 he recorded his first single, Why Am I, in New York, described by Billboard magazine as the "expressive warbling of a moody ballad, by the label's new 16-year-old chanter".
Paul recorded several more discs before being drafted, in 1957, into the US Army, where he served alongside Elvis Presley in Germany and performed with the 7th Army Band. In 1959, after being discharged, he returned to the music scene and had a spell in the ever-changing line-up of Harold Melvin's popular Philadelphia soul group, the Blue Notes. During this time, Paul met and befriended Marvin Gaye, who was also working as a jobbing singer with the emerging soul groups.
In the late 1960s Paul and his wife (also his manager), Blanche Williams, were approached by Kenny Gamble who, with his songwriting and producing partner, Leon Huff, would go on to create the Philadelphia soul sound for their label, Philadelphia International Records (PIR).
Gamble signed Paul to his label and in 1968 he released his first album, Feelin' Good at the Cadillac Club, although it was not a commercial success. With Gamble & Huff's formation of PIR, however, Paul found himself joining a family of new acts who combined soul and jazz with funky dance grooves.
In 1972 he released the album 360 Degrees of Billy Paul, on which he had included Me and Mrs Jones. The yearning lyrics of the song - which was written by Gamble and Huff with Cary Gilbert, and has since been covered by artists ranging from Michael Buble to the actress Sandra Bernhard - were brought to life by Paul's effortless and occasionally soaring vocals. It became the torch song for adulterous spouses and reached No 1 in the US charts in 1972 and was a British Top 20 hit the following year. It sold two million copies and went on to win Paul a Grammy Award.
It was also the first No 1 for PIR, and it was expected that Paul would soon release another smoochy soul classic. It was, therefore, somewhat surprising to Paul when he followed it up with Am I Black Enough for You?
The song failed to achieve the crossover success of Mrs Jones and was later adopted by the Black Power movement.
Paul revealed that he had not wanted to release the single. "But the company felt I had to get over to the black audience this time round," he recalled in 1973. "And there can be no arguing about that - the record is one of the top sellers in the black areas and one of the most requested records around the stations. I don't really think anybody expected it to be a pop hit."
Commercially it proved difficult for Paul to recover from such an overtly political track, and he never achieved the recognition or mainstream fame of some of his contemporaries.
His single, Let's Make a Baby (1976), also attracted controversy, although this time because of lyrics which were regarded as too explicitly sexual. Some American radio stations tried to ban the song.
In 1977 Paul recorded a version of Paul McCartney's Wings song Let 'Em In, changing the lyrics to include a list of civil rights leaders, including Martin Luther King and Malcolm X. That same year he joined Lou Rawls, Archie Bell, Teddy Pendergrass, Dee Dee Sharp Gamble, and Eddie Levert and Walter Williams as part of the Philadelphia International All-Stars singing the outrageously groovy Let's Clean Up the Ghetto.
Paul continued to record in the late 1970s and 1980s, playing at small venues and festivals into his 70s.
In 2009, he was the subject of a documentary, Am I Black Enough for You?, in which it was revealed that he had had a spell as a cocaine addict before recovering with the help of his wife. The couple were described as coming across as "a jazzy Darby and Joan". Paul is survived by his wife and their two children.