There are many that can be noted but I will add two. Danny Seraphine -original drummer for Chicago and Floyd Sneed-original drummer for the original Three Dog Night.
Danny had great chops that could adapt to any style, jazz, rock, pop you name it. An integral part of the Chicago sound.
Floyd had style unlike any other that added to the uniqueness of the sound of Three Dog. He, bassist Joe Schermie, guitarist Michael Allsup and keyboardist Jimmy Greenspoon created one hellova rhythm section.