Terry Kath definitely way up there near the top, imo.
Early Chicago rips, amazing meld of rock/hard rock/experimental/jazz/psychedelic and Kath covers all the bases.
It’s a shame that these days Chicago is mostly associated with the post Kath Peter Cetera schlock.
Speaking of Peter Cetera, if anyone hasn’t had the pleasure, look up “Yacht Rock” on youtube. Hilarious take on the late 70’s into the 80’s pop music scene. Michael Mcdonald is portrayed as the protagonist, and he later said that even though Yacht Rock is a parody, there’s a lot in there that they actually got right.