You hear the word "fierce" a bit too much in show business today. It is bandied about by aspiring young artists to describe what previous generations would have called "cool" "rad" or if you are old enough, "groovy." While the term fierce is thrown around slapdash, we use it only in the most serious of circumstances and never has it been more warranted than now.
Kenneth Miller is FIERCE. In the all-caps, bold and italics sense of the word. So fierce in fact, that he played a swing, in ART's production of Prometheus Bound. He is a staple at American Repertory Productions such as the Donkey Show.
The Oxford English Dictionary defines fierce as showing a powerful and heartfelt intensity. No better way to describe Kenneth Miller.