Steely Dan co-founder and guitarist Walter Becker has died aged 67, according to a post on his official website.
No cause of death has yet been announced, but Becker had missed gigs in July to recover from an unspecified condition.
Jazz-rock band Steely Dan, which Becker founded with Donald Fagen, have sold over 40 million albums and were inducted into the Rock and Roll Hall of Fame in 2001.
The two met while studying in New York, before relocating to California and forming the group along with Jeff Baxter and Denny Dias, drummer Jim Hodder and singer David Palmer.
Steely Dan released seven albums during their original tenure between 1971 and 1981, including Aja, Katy Lied and Pretzel Logic, but reunited in 1993 and had continued touring since.
Outside of the band, Becker was involved in production work, and released two solo albums, the last of which, Circus Money, was released in 2008.
In a statement on Twitter, Donald Fagen has said of his late bandmate, "he was smart as a whip, an excellent guitarist and a great songwriter".
Fagan also stated he "intends to keep the music we created together alive as long as I can with the Steely Dan band".