From Ruffin's Wikipedia entry:
In 1961, Jimmy became a singer as part of the Motown stable, mostly on sessions but also recording singles for its subsidiary Miracle label, but was then drafted. After leaving the Army in 1964, he returned to Motown, where he was offered the opportunity to join the Temptations to replace Elbridge Bryant. However, after hearing his brother David, they hired him for the job instead so Jimmy decided to resume his solo career. Jimmy Ruffin recorded for Motown's subsidiary Soul label, but with little success.
In 1966, he heard a song about unrequited love written for The Spinners, and persuaded the writers that he should record it himself. His recording of "What Becomes of the Brokenhearted" became a major success. The song reached #7 on the Billboard Hot 100 and #6 on the R&B Chart. It also initially reached #10 in the UK singles chart, rising to #4 when it was reissued in the UK in 1974. "What Becomes of the Brokenhearted" remained Ruffin's best-known song.