pacesetter

noun

1. One who or that which determines the rate of action through leading.

   “It’s all been a dreadful embarrassment, but why should anyone outside Germany be concerned? Because Documenta was always a pacesetter — and this year’s edition certainly put its finger on a larger shift, seen too in our museums, our art schools and our magazines, away from aesthetic ambition and intellectual seriousness and toward the easier comforts of togetherness, advocacy and fun.”