Showing up in The Fifties and The Sixties, soul was developed by African-American musicians by combining elements of Gospel and Rhythm And Blues. The result was something that sounded a lot like Gospel but (usually) without the religious themes.
Soul had a powerful effect on both Rock & Roll and modern Pop, and was the leading form of music for African-Americans until Funk (itself heavily influenced by soul) came onto the scene in the early Seventies. Soul kept on; it eventually became nigh-indistinguishable from its forbear R&B (Rhythm And Blues) as, in the face of the rise of Hip Hop, the term started to be used for "any music made for and by black people that still has melodic singing." Purists cringed, of course, but alas, there was nothing to be done.
Every now and then, soul makes some kind of resurgence. For some reason, white folks tend to really like doing these things; this is generally called "blue-eyed soul," since calling it "white soul" would be a touch obvious. Strangely, the British are the most likely to try a soul-influenced sound: David Bowie broke into the American market after he switched from glam rock to soul (with the New Sound AlbumYoung Americans, recorded in Philadelphia), and two of the biggest soul acts of the past decade are Amy Winehouse and Adele, both as English as they come. Oh, and the term "plastic soul" itself came from an older African-American's characterization of The Rolling Stones (which prompted The Beatles to name their next album Rubber Soul, 'cos, wouldn't you know it, they were high at the time and thought that was funny).
Britain is strongly associated with the mod-oriented northern soul scene of the 1960s and early 1970s, which grew out of the dance clubs in cities like Manchester and Wigan and was sustained by DJs who specialized in tracking down extremely rare soul tracks which never quite gained mainstream popularity. Many British pop stars who kicked off their careers at the onset of the 1980s, including Elvis Costello, The Specials and Dexys Midnight Runners (who took their name from a popular northern soul mod amphetamine which gave its users the energy to dance all night) were active participants in or admirers of the northern soul movement.
Soul Train started (predictably enough) presenting soul acts on television, à la American Bandstand. As the black community's tastes in music changed, Soul Train changed its tune a bit (and at some point became inextricably — and ratherembarrassingly — linked with Disco), but the roots were still fairly obvious down to the end.
Please do not confuse with the Discworld novel.
Famous soul acts include (in roughly chronological order):
Ray Charles: Credited as one of the inventors of soul, Ray was probably the first artist to fuse rhythm and blues with gospel; many of his early songs, including "This Little Girl Of Mine" and "Hallelujah, I Love Her So", borrowed melodies from gospel songs. His 1954 hit "I Got A Woman" is frequently described as the first soul song.
Sam Cooke: Along with Ray, Sam Cooke was one of the inventors of the genre, although his songs probably leaned towards gospel moreso than R&B. Although he died young, he left a legacy of great recordings which have been widely covered (most notably by Otis Redding) and continue to influence aspiring singers. His landmark recording "A Change Is Gonna Come" (inspired by the music of Bob Dylan) is often credited as one of the first really socially conscious soul songs.
Little Richard: Actually signed to a record company who wanted to market him as a rival to Ray Charles. Although he's best known as one of the first and best Rock & Roll stars of The Fifties, his energetic vocal performances and gospel-singing background were very influential on subsequent performers; notably, he was Otis Redding's favourite singer.
James Brown: His stage names have included "the Godfather of Soul" and "Soul Brother Number One" and he essentially became the number one performer in the genre after Sam Cooke died and Ray Charles began to diversify his sound. A major connector between Soul and Funk, his Live At the Apollo album is recognised as the starting point for the latter style.
Aretha Franklin: Well, yeah. The Queen of Soul. Like Ray, Sam Cooke and James Brown, she began her singing career in the late 1950s, mainly performing straightforward gospel-influenced R&B, but when the sixties rolled around she developed the powerful, passionate style that she's famous for.
Motown: One of the most successful exponents of soul in the history of popular music, Motown was founded by Berry Gordy, who had written songs for Jackie Wilson until he realised there was more money to be made on the business side of music. Motown and its subsidiary labels were famous for the incredibly high standard of musicianship in its house band (the Funk Brothers), the factory-like production of new songs to ensure crossover appeal and, perhaps most importantly, spearheading the racial integration of pop music. Some of the famous acts signed to the label include:
Stevie Wonder: Originally signed as "the twelve-year old genius", Wonder was one of the first Motown acts to take real risks with his music and eventually managed to wrest creative control from Berry Gordy, a move which would inspire many of his contemporaries to do likewise.
Marvin Gaye: Renowned as one of the best soul singers of them all, Gaye got his start as a session musician and songwriter before he stepped into the spotlight himself. Like Wonder, he struggled for creative freedom and won, and the result was the expansive, socially-conscious Concept AlbumWhat's Going On.
The Supremes: In some respects the Spiritual Successor to pre-Motown Rock & Roll girl groups like the Shirelles, the Supremes were one of the primary vehicles of the Holland-Dozier-Holland songwriting and production team. During the sixties they were second only to The Beatles as one of the most popular groups in America and their influence on contemporary performers (such as the late Amy Winehouse) cannot be underestimated. After they split, lead singer Diana Ross became a star in her own right.
The Temptations: Originally presented as a clean-cut Boy Band, the Temptations were one of the most successful all-male vocal groups to perform on the label. In the late 1960s, they became a vehicle for the staff songwriters experiments with psychedelic influences, leading to the creation of a whole new subgenre known as psychedelic soul.
The Four Tops: Another Holland-Dozier-Holland group, the Four Tops were in some respects presented as rivals to the Temptations. They're best known for hits like "Reach Out, I'll Be There" and "It's the Same Old Song" which showcased the powerful lead vocals of Levi Stubbs; while their songs had the same polished production as their labelmates, Stubbs's gritty, gutsy voice helped to set them apart.
The Jackson 5: You know who these guys are. Yes, it's the group that featured Michael Jackson and his brothers, put together largely on the initiative of their father, Joe. Even though they were very successful in the early 1970s and had several hits that are still remembered, today they're probably thought of pretty much as "Michael Jackson's old group".
Junior Walker: Originally a session musician, saxophonist and singer Junior Walker was something of an oddity in the Motown stable. With his backing band, the All-Stars, he recorded hits like "Road Runner" and "Shotgun" which showcased his phenomenal talents on the sax. His music was less over-produced than other Motown artists; in fact it sounded almost like it belonged on...
Stax Records: Based in Memphis, Stax typically had a rawer, grittier, harder-edged southern sound in contrast to the smoother, sweeter output of Motown artists. Having enjoyed great success in the early 1960s, it suffered several blows toward the end of the decade (including the death of its biggest star and the cessation of its contract with its distributor, Atlantic Records, which left it without a back catalogue) until the Wattstax event revived its fortunes. Like Motown, Stax attempted to branch out into fields beyond music and sought to encourage social justice and racial integration, but shady financial dealings and money mismanagement ended up killing the label in the mid-1970s. Famous Stax recording artists include:
Booker T. and the MG's: A racially integrated instrumental R&B group consisting of keyboardist Booker T. Jones, drummer Al Jackson, guitarist Steve Cropper and bassist Donald "Duck" Dunn, the Stax house band was most famous for its hit "Green Onions" but were also highly-skilled session musicians who played on nearly every hit cut by the label. In addition, Jones and Cropper were amongst the most prolific songwriters associated with southern soul.
The Memphis Horns: Originally a trio featuring Charles "Packy" Axton and Andrew Love on saxes and Wayne Jackson on trumpet, they were the other half of the Stax session team. Originally they were the frontline of an earlier instrumental group called the Mar-Keys, which also featured all four members of Booker T. and the MG's and recorded the R&B hit "Last Night". They're responsible for many, many famous horn lines, including those from "Hold On, I'm Comin'", "I Can't Turn You Lose" and "Sweet Soul Music".
Otis Redding: The King of Soul himself, Otis was described by Steve Cropper as the collective Team Dad for Stax Records in spite of his youth. The most consistently successful artist on the label, he was on the verge of major crossover success when he died in a plane crash in 1967. His most famous songs were the posthumous hit "(Sittin' On) The Dock Of the Bay" and his explosive cover of "Try A Little Tenderness".
Sam & Dave: Known as the Double Dynamite, the Dynamic Duo and the Sultans of Sweat, the Vocal Tag Team of Sam Moore and David Prater were one of the grittiest, most gospel-influenced acts in all of soul music. While they were signed to Atlantic Records, they were sent to Memphis to record, and became famous for turning songs like "Soul Man" and "Hold On, I'm Comin'" into soul staples. The collapse of Stax's distribution arrangement with Atlantic, which coincided with the death of Otis Redding, saw them leave Memphis to record in New York, which proved to be a turning point for the label.
Wilson Pickett: While not officially a Stax artist (he was another Atlantic signing), Pickett captured their style of Memphis soul as well as any other soul shouter, recording big hits like "In the Midnight Hour" (which he co-wrote with Steve Cropper) and "Land Of 1000 Dances" at the Stax studios. After the end of the Stax-Atlantic relationship, he was sent to record in Muscle Shoals, where he was backed by Duane Allman and injected southern rock influences into his music. Toward the end of his hitmaking career, he also dabbled in the nascent Philly soul idiom which would subsequently influence singers like Luther Vandross.
Isaac Hayes: Originally a session musician and songwriter who penned most of Sam & Dave's most memorable songs in partnership with David Hayes, Hayes became famous in his own right when his Hot Buttered Soul LP turned out to be an unexpected success and made him Stax's biggest star after Otis's passing. His greatest achievement was the soundtrack for the Blaxploitation film Shaft, which won him an Academy Award. In the 1990s he was introduced to a younger audience as the voice of Chef in South Park.
Percy Sledge: Never associated with Stax, although he sounded like a halfway point between that label and Motown, Sledge is best remembered for the song "When A Man Loves A Woman", which earned him a reputation as a One-Hit Wonder (even though he had other hits on the R&B charts). Much like Ray Charles, he was notable for integrating country influences into his style.
Rev. Al Green: Most famous for the song "Let's Stay Together", Green kept southern soul alive during the 1970s when funk music had started to become more popular in the African-American community. However, his decision to leave secular music for a while to concentrate on gospel music and his ministry around the same time Stax went under was arguably the death knell for the genre for several years.
Luther Vandross: One of the last major exponents of soul as such (everybody afterward was "soul, R&B, funk, and jazz" on account of blurring distinctions), and a pioneer of the Philadelphia Soul subgenre. He got his big break as a backing vocalist on Young Americans, helping Bowie make the aforementioned transition into soul that made him marketable on the left side of The Pond.
Amy Winehouse: Responsible for kicking off a major soul revival in the mid to late late 00's, in not only the United Kingdom but all around the world. Her music directly inspired and paved the way for other notable soul singers of that period including Adele, Paloma Faith, Shannon Jones and the Dap Kings, Duffy, Rebecca Ferguson, Azaelia Banks, Rebecca Ferguson and Emilie Sande. Many have dubbed the recent influx of British soul singers enjoying success on the American charts, which was led by Winehouse, a third British Invasion or a British Soul Invasion.