McDonald's said its "chief happiness officer" had to start encouraging children to exercise.
The new look Ronald wears tighter fitting clothes in the ad, not the usual baggy yellow clown togs.
It's a lot like the Honey Monster ads, but with a much more frightening central character...
The ads will be backed up with a print campaign and will go global on the autumn.
According to McDonald's, the TV ad "shows kids how much fun they can have when they activate their bodies, their minds, and their imaginations."
Ronald McDonald is now said to be a "global ambassador of fun, fitness and children's well-being".