To one Motown staffer, they sounded "like doves" together. Marvin Gaye had been paired with other duet partners -- Kim Weston, Mary Wells -- but he'd never known creative bliss like he did when he started singing with Tammi Terrell.

Born Thomasina Winifred Montgomery in 1945, the young singer began her recording career as Tammy Montgomery at the age of 16. Spotted by James Brown, she soon joined the soul man's revue, recording two of his songs. Her volatile affair with the singer, however, led to a quick departure. By 1965, she was singing with Jerry Butler when she was recruited by Motown's Berry Gordy.

At the Detroit label, the vivacious young singer, now renamed Tammi Terrell, began a rocky relationship with David Ruffin of the Temptations. Artistically, she was soon paired with Gaye, with the two recording Nick Ashford and Valerie Simpson's 'Ain't No Mountain High Enough' in early 1967. Their extraordinary chemistry was evident from the beginning, and Gaye and Terrell released seven more Top 40 singles in the next two years, including such Motown classics as 'Ain't Nothing Like the Real Thing' and 'You're All I Need to Get By.'

Terrell's relationship with Ruffin was by all accounts contentious, and they broke up often. Her other romances weren't much better: Another boyfriend allegedly pushed her down a staircase. Meanwhile, she had a platonic, sisterly relationship with Gaye (who was married to Gordy's sister Anna), though their songs together epitomized the notion of selfless love. Together they created "two characters," as Gaye told his biographer: "two lovers that might have been in a play or a novel."

Terrell had been complaining of migraines when, in the summer of 1967, she collapsed in Gaye's arms while performing at a Virginia college. Doctors discovered a brain tumor, one that would require eight operations over the next three years.

Terrell's failing health made performing increasingly difficult; some of her new releases with Gaye were actually existing solo demos with Gaye's vocals added after the fact. For their third album, 'Easy,' the label secretly substituted Valerie Simpson for the ailing singer on several tracks.

As her health deteriorated, Terrell suffered memory loss and was confined to a wheelchair. Motown tried to reassure fans, sending Ruffin out to claim she would recover. But on March 16, 1970, Tammi Terrell's body gave out to cancer. She was 24.

Marvin Gaye was inconsolable, reportedly sobbing by his singing partner's casket at the funeral. Having effectively stopped performing since her onstage collapse, he would remain in seclusion for some time to come. Terrell's death and Gaye's brother's tales from Vietnam combined to put the singer in a despondent frame of mind, which had unexpected consequences for his career: His next album, the broken-hearted 'What's Going On,' would be his masterpiece.

Years later, he would remember his devastation at the loss of Terrell: "It was a deep vibe ... as though she was dying for everyone who couldn't find love." Though Gaye remained a star for more than a decade, he was never again as unburdened as he'd been when singing with Terrell. Drug and tax problems led to a brief period in the late 1970s when he lived in a van in Hawaii, before the remarkable comeback of his smash hit 'Sexual Healing.' That success, like Terrell's, was short-lived. On April 1, 1984, the singer was shot and killed by his own father.