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.”

With Parazaider, Chicago became one of the most distinct and prolific bands of their era, signing with Columbia Records and dropping 10 albums in the ’70s alone. They received critical acclaim early as Chicago Transit Authority, and the group’s eponymous debut album would subsequently go double platinum. They changed their name again for their sophomore effort Chicago, which earned a Grammy nomination for album of the year.

The group earned their first number one song in 1976 with the smash “If You Leave Me Now,” which also won the band its first Grammy award, for best pop performance by a duo or group with vocals. The band remained active for decades after, and they found massive commercial success in the early ’80s with “You’re The Inspiration.”

The group was officially inducted into the rock and roll hall of fame in 2016.

Parazaider’s daugther, Felicia Parazaider, posted in emotional tribute to her father on Facebook on Wednesday as well, saying that she couldn’t be there when her father officially passed but that “he went peacefully.”

“Thank you for loving my father, even if you didn’t personally know him,” she wrote. “I know that many of you loved him. I’m in shock and disbelief and yet not at all. This was the worst six years. The hardest season of my life. And I’m so grateful that my dad is not suffering anymore. I love you poppy, my Pal. You coloured our world. God bless you, you dear soul.”

“We are forever grateful for his contributions,” the band wrote on Wednesday. “Perhaps his greatest gift was bringing people together. This amazing music may have never been heard had it not been for Walt’s vision.”