Jimmy Pankow of Chicago talks about changing people's perception of what a rock band was.

When Chicago first debuted (is that redundant?), some rock
purists were hesitant to call it a "rock band" because it had a
built-in horn section (Jimmy Pankow on trombone, Lee Loughnane on
trumpet, and Walter Parazaider on saxophone and flute). 
Here, Dan Markus (a trombonist himself-back in the day) brings
the subject up with Chicago founding member Jimmy
Pankow.