Walter Becker, guitarist and co-founder of the group Steely Dan, died Sunday at the age of 67.

A post on Becker’s official website confirms the news, although no cause of death has been revealed.

In July, Becker was unable to perform with the band for a number of shows while he recovered from a procedure, according to an interview Steely Dan co-founder Donald Fagen gave with Billboard.

Fagen and Becker, who was born and raised in Queen, NY, founded the group in 1972. Their hits singles included “Reelin’ In the Years,” “Dirty Work” and “Rikki Don’t Lose That Number”. Although the band split up in 1981, they reformed in 1993 and released two additional albums, including the Grammy-winning Two Against Nature.

On Sunday, Fagen wrote a touching tribute to his friend, calling Becker “smart as a whip” and “an excellent guitarist and a great songwriter”. Read the full statement in Rolling Stone.