You've seen their viral music videos online, and so apparently has the president.

OK Go, the treadmmills-to-Pilobolus YouTube favorites, performed at Barack Obama's 50th birthday bash this week at Chicago's Aragon Ballroom. Two days later they were playing to Lollapalooza.

We caught a few minutes with OK Go singer Damian Kulash backstage at Grant Park on Friday to talk about his Marilyn Monroe impression: