Her unexpected death was attributed to cardiac arrest and was announced on social media by her partner, Prudence Fenton.
Ms. Willis, who was nothing if not eclectic, exuberant and eye-catching, wore garish outfits of clashing patterns and bright colors, often with gold or pink sneakers. She cut her hair in a lopsided style that was long on one side, short on the other.
She filled her pink, Art Deco-style Los Angeles home with an overflowing collection of kitsch — from board games to celebrity-endorsed shampoos — and her own art, which she cobbled together from assorted odds and ends. She chronicled her life on film virtually every day for the past 40 years and gave outrageous parties where famous actors and musicians wore pajamas, dressed in trash bags and played silly games created by Ms. Willis. (Cher once won the “Tampax Toss.”)
“I’m a serious party thrower,” Ms. Willis told the New York Times in 2018. “I’ll tell you, that’s my No. 1 skill. I always had a music career, an art career, set designer, film and video, technology. The parties really became the only place I could combine everything.”
Still, she was best known as a songwriter who had an instinctive feel for the upbeat tunes that kept the country dancing in the 1970s and 1980s. She could not read music or play an instrument, but in collaboration with other tunesmiths she co-wrote several Top 10 hits, including “September” and “Boogie Wonderland” by Earth, Wind & Fire, the brassy, dance-all-night band of the 1970s that received the Kennedy Center Honors earlier this month.
After Ms. Willis released her first and only album, “Childstar,” in 1974, her songs were noticed by Bonnie Raitt and other performers, who asked her to write for them. She became known as the “Rock Doc,” tweaking songs (often without credit) for better-known artists such as Ray Charles, James Brown, George Benson and Patti LaBelle.
But by 1978, she said in a video interview, “I was on food stamps, medical assistance, really as close as you could be to welfare without actually being on it.”
At that low point, she received a call from Maurice White, the leader of Earth, Wind & Fire, who asked her to help write songs for the group.
“As a white Jewish girl getting a break, you could not get better than Earth, Wind & Fire,” Ms. Willis told NPR in 2014. “And as I opened the door, they had just written the intro to ‘September.’ And I just thought, dear God, let this be what they want me to write because it was obviously the happiest-sounding song in the world.”
The opening guitar-and-brass riff was written by the group’s guitarist, Al McKay, and White had an idea for how he wanted the song to begin: “Do you remember the 21st night of September?”
Ms. Willis worked with White and McKay to refine the tune and add more lyrics:
Our hearts were ringing
In the key that our souls were singing
As we danced in the night
Remember how the stars stole the night away
Released in 1978, “September” hit No. 8 on the Billboard pop chart and No. 1 on the R&B chart. It has since acquired a permanent afterlife as a bouncy, feel-good tune played at countless weddings, graduations, proms and dance parties.
One phrase White repeated throughout the song drove Ms. Willis crazy: “Ba-dee-ya, do you remember? Ba-dee-ya, dancing in September. Ba-dee-ya, never was a cloudy day.”
“I remember at the final vocal session pretty much being down on my knees next to him begging, ‘Please change ‘Ba-dee-ya,’ ” Ms. Willis told NPR. White kept the nonsense syllables in the song, and Ms. Willis learned what she called “my greatest lesson ever in songwriting”: “Never let the lyric get in the way of the groove.”
She went on to co-write most of the songs on Earth, Wind & Fire’s 1979 album, “I Am,” including the Top 10 hit “Boogie Wonderland.” A few years later, she helped write “Neutron Dance,” which hit No. 6 for the Pointer Sisters in 1985.
The song also inspired the Soviet Union’s official Communist Party newspaper Pravda to condemn Ms. Willis as a “nuclear gravedigger” and “self-declared priest of nuclear art.”
“All I could think of,” Ms. Willis said at the time, “was, How do they even know who I am? Was the KGB following me?”
In 1986, Ms. Willis shared a Grammy Award for her work on the soundtrack of the film “Beverly Hills Cop,” then scored another hit with the 1987 song “What Have I Done to Deserve This?,” which reached No. 2 in the United States and the United Kingdom for the Pet Shop Boys, with Dusty Springfield.
Perhaps her most widely heard tune, “I’ll Be There for You,” on which she collaborated with several other songwriters, debuted in 1994 as the theme for the sitcom “Friends.” It became a Top 20 hit for the Rembrandts.
For several years, Ms. Willis’s songwriting took a back seat to her artwork, party-giving and her early adoption of the Internet. She turned her kitsch collection — “The worse something is, the more I love it” — into an online museum, and her interactive website, Willisville.com, was something of a 1990s forerunner to modern-day social media platforms. Among other endeavors, she wrote a column for Details magazine, directed music videos for Blondie and the Cars and worked as a set designer.
Ms. Willis returned to music in the early 2000s, after a theatrical producer asked her for suggestions of people who could compose a musical version of “The Color Purple.” She suggested herself.
With two other songwriters, Brenda Russell and Stephen Bray, Ms. Willis wrote both words and music for the musical play, which ran on Broadway from 2005 to 2008. The score was nominated for a Tony Award. After a Broadway revival beginning in 2015, the theatrical album of “The Color Purple” netted Ms. Willis her second Grammy Award.
Alta Sherral Willis was born Nov. 10, 1947, in Detroit. Her mother was a schoolteacher, and her father ran a scrap yard, where Ms. Willis spent weekends “climbing 40-foot piles of old toilets and crushed cars.”
During the early years of the Motown music boom in Detroit, Ms. Willis said she would sit outside the studio and listen through the walls to recording sessions, “which is how I became a songwriter.”
She graduated from the University of Wisconsin at Madison in 1969, then moved to New York, where she wrote copy for record companies and composed songs.
After settling in Los Angeles, Ms. Willis claimed to be the mentor and manager of an artist named Bubbles. She sold more than 1,000 paintings and sculptures before revealing that Bubbles was, in fact, one of her alter egos.
“My whole career is based on two truths,” she said in 1987. “What can’t possibly happen, happens. And what should be happening, doesn’t. There’s no middle ground.”
In recent years, Ms. Willis went onstage with a one-woman show about her life and worked on an ambitious, but unfinished, video and recording project built around the musical life of Detroit. She was inducted into the Songwriters Hall of Fame in 2018.
Besides Fenton, an animator who worked on “Pee-wee’s Playhouse,” survivors include a sister and a brother.
In her will, Ms. Willis requested that her house be preserved in all its outlandish glory, with everything left in its place, including the bowling balls planted in the garden.
“Someday, someone will happen upon all this stuff and say, ‘Oh, this chick had it together,’ ” she told The Post in 2015. “Maybe people will finally know who I am.”
Read more Washington Post obituaries