The most important folk singer- I believe it would be Pete Segger.

The most important outside of folk- I going to take a left from everyone else and say Earth Wind and Fire-

Six Consecutive Double Platinum Albums ( 2 million ) "That's The Way Of The World" "Gratitude" "Spirit" "All N' All" "Best Of ...., Vol. I" "I Am" First Black Act To Top Billboard Pop Single And Album Charts Simultaneously (May 24, 1975) "Shining Star" (Single) "That's The Way Of The World" (LP) First Black Act To Receive Columbia Records Crystal Globe Award Signifying Five (5) Million Albums Sold Outside Home Country. Top Selling Band in Columbia Records History First Black Act To Tour With Completely Self-Contained Stage Presentation. (Staging, Lights, Sound, Costumes, Trucking, Etc.) First Black Act To Headline An Arena Tour Around The World Without An Opening Act - 1979 (US, Europe, Japan). First Black Act To Bring Full Production Show To South America - 1980 First Black Act To Receive Madison Square Garden Gold Ticket Award For 100,000 Tickets Sold.

Pretty remarkable! Not to many will agree they are the most important preformers, but they accomplished a lot!