Billy Cobham was the first drummer that made me go "WTF is that he's playing!" and want to break and burn my drumsticks!!
Ditto. My first exposure to his playing and style was listening to the Mahavishnu Orchestra. I was playing in a horn band covering Tower of Power and Chicago at the time, and felt the same "Holy $#!t, WTF" revelation when I heard him deliver what we now call "fusion". I knew at that moment that there was a level of drumming I would never be able to replicate, and that even if I was able to come close to copying some of his moves, I would never possess the genius to originate such stuff.
When MO's "Visions of the Emerald Beyond" came out, I was dismayed that Cobham had been replaced with Michael Walden, but Walden certainly filled Cobham's shoes very well with his own "WTF" moments. Cobham was a true pioneer who blazed a trail that others simply followed.