Walter Parazaider, co-founder, saxophonist and flautist in the rock band Chicago, has died following a battle with Alzheimer’s, the band confirmed on Wednesday. He was 81.

“Chicago is heartbroken at the sad news of Walter Parazaider’s passing this morning,” the band said in a statement on Wednesday. “We extend our deepest condolences to his family, friends and countless Chicago fans who are all grieving his loss today. A Rock & Roll band with horns was Walt’s idea. He put the band together and they rehearsed in the basement of his mother’s home. He is also the one who did the hard work to book shows for the young, unknown band, performing top 40 covers at local bars in and around Chicago.”

Parazaider first helped form the group in 1967, back when the band was first called The Big Thing. He played on two dozen Chicago albums from 1967 through 2014, and he performed live with the band as well until retiring due to health issues back in 2018.

As the band suggested, Parazaider was a key part of the group’s sound, with the Chicago’s jazzy horn section arguably its signature feature. Parazaider’s playing is fully on display on the band’s biggest hits including “Saturday in the Park” and “25 or 6 to 4.”