Walter Becker, the guitarist, bassist, and co-founder of the indelible duo Steely Dan, has died at age 67. News of his passing was announced on Becker's website on Sunday morning. A cause of death was not mentioned.

When Becker did not attend Steely Dan's Classic East and West concerts earlier this summer, Steely Dan co-founder Donald Fagen told Billboard that "Walter's recovering from a procedure and hopefully he'll be fine very soon."

The two began their decades-long partnership in 1966, as Bard College students. "We were both jazz and blues fans as kids, which was kind of unusual at the time," Fagen said of Becker, in a 2008 interview with Gothamist. "At the time there were a lot of different kinds of music and it was all novel at the time; soul music was basically invented when we were in high school and that grabbed our attention. And we just combined all those things into the kind of music that we like."

"We were both also interested in literature," Fagen added. "At the time, I guess we were of the generation that began what they used to call black humor, which they now just call humor. It was a kind of dark humor that was typical of the upcoming writers like Kurt Vonnegut and Bruce Jay Friedman and, on a more sophisticated level, Vladimir Nabokov, who was a big influence."

After college, the two moved to Brooklyn, where they attempted to sell their music at the Brill Building, and were able to get some work as studio musicians for Jay and the Americans. They also provided the soundtrack to a few films, including the low-budget Richard Pryor movie You've Got to Walk It Like You Talk It or You'll Lose That Beat.

But they struggled to find success in New York, so in 1971 the duo moved to Los Angeles, where they were quickly offered a contract after impressing ABC-Dunhill President Jay Lasker. The original lineup of Steely Dan—named after a dildo in Naked Lunch—featured Becker on bass and Fagen singing and playing keyboard, alongside guitarists Denny Dias and Jeff "Skunk" Baxter, and Jim Hodder on drums.

Their 1972 debut Can't Buy a Thrill included hit singles "Reelin' in the Years" and "Do It Again," along with the radio-friendly "Dirty Work," sung by David Palmer, who'd end up leaving the band shortly after.

The Steely Dan lineup shifted several more times over the course of the 1970s, and only Becker and Fagen remained as core members. Together, they'd oversee the creation of five albums over the next five years, with an impressive catalogue of hits such as "Rikki Don’t Lose That Number," "Haitian Divorce," and "My Old School,"—a sardonic remembrance of getting raided by cops for smoking pot while in Bard.

The group's biggest success came on 1977's Aja, one of the earliest American albums to sell over 1 million copies, on the strength of hits such as "Peg" and "Deacon Blues." (There's also the very funky "Black Cow", featuring a memorable homage to the still-standing Rudy's Bar & Grill on Ninth Avenue in Hell's Kitchen.) Widely hailed for its complex and pristine sonic detail, the album would go on to win a Grammy for engineering, and eventually take the 145th spot on Rolling Stone's The 500 Greatest Albums of All Time list.

In 1980, Steely Dan would release the critically lauded Gaucho. The album, and the string of tragedies that surrounded it (including the overdose death of Fagen’s girlfriend Karen Stanley), "finished us off," according to Becker, and the two partners went their separate ways for much of the decade. They reunited in 1993 for Two Against Nature—another Grammy award-winner—and in 2003 released Everything Must Go, featuring Becker's first-ever lead vocal on the song "Slang of the Ages."

They've since toured extensively, including a nearly two-hour-long set in Greenwich, Conn. earlier this year, where Becker can be heard saying "All I care about is right here, right now, tonight," before thanking "the most incredible fans in the whole wide world."

In a heartfelt statement released Sunday morning, Fagen remembered Becker as "hysterically funny" and an "excellent guitarist and great songwriter."

"I intend to keep the music we created together alive as long as I can with the Steely Dan band," the statement concludes.

Others paid their respects to Becker across the internet on Sunday: