"His music is unmatched in terms of great songwriting," Verdine White of Earth, Wind and Fire said after learning of his friend's death.
"They had magic and that's what creates those wonderful hits, that magic," White added. "Without those songs, those artists wouldn't have been able to go to the next level."
Others in the music industry also mourned the loss. On Twitter, Alicia Keys wrote, "I'm so sad that he's gone. ... So many of the greatests are going to a greater place ... what a legacy of infectious music ... man!"
Ashford and Simpson's relationship stretched more than four decades. They met in 1964 in a New York City church. Ashford, a South Carolina native, had come to the city to pursue a dance career. Simpson was a music student, and after connecting with her, they decided to start to write songs together.
"They were always comfortable with each other and they made all of us comfortable, because they were comfortable," White said.
Their first major success occurred when they came up with "Let's Go Get Stoned" for Ray Charles. The bluesy, gospel-tinged song became a huge hit for Charles, and soon, they came to the attention of Motown Records and began penning hits for their artists.
They started out writing soulful, romantic works for the duo of Gaye and Terrell that would become instant classics, like "Your Precious Love," and "Ain't Nothin' Like The Real Thing." In fact, "Ain't No Mountain High Enough" was originally their hit, until Ross later rerecorded it with a new arrangement that had sweeping pop grandeur and made it her signature song.
Ross may have been their greatest muse: With her, they had some of their biggest songs and helped give her career-defining hits that would distinguish her solo career apart from The Supremes. Among the songs Ross made hits were "Reach Out and Touch," ''The Boss," ''My House," and "Missing You," a tribute to the late Gaye and others. They also composed some of the music for "The Wiz," the movie musical that starred Ross and Michael Jackson.
In an industry where marriages and partnerships are fleeting, Ashford and Simpson stood the test of time.
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"The thing is they were married and working together, that was what was special about them. Everybody admired that," White said.
The duo, married for 38 years, helped sell millions of records for several artists. They also had success as their own entity, but despite "Solid As a Rock," their songs were dwarfed by those they penned for others. They continued to craft hits even into the new millennium: They are credited as co-writers on Amy Winehouse's "Tears Dry On Their Own."
In recent years, the pair continued to perform. They also were owners of the New York City restaurant Sugar Bar, where many top names and emerging talents would put on showcases.
In 2002, Ashford & Simpson were inducted into the Songwriters Hall of Fame.
Ashford is survived by his wife and two daughters. Rosenberg said there is no information yet on funeral arrangements.
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