Someone working within their field of expertise, with the tools to get it done, and without the typical roadblocks that stand in the way. Hopefully you've been there and know how it feels.
And maybe you've also been at the other side of the spectrum, working with an ever-changing, badly designed and documented piece of technology, with many surprise problems biting you in the ass, ever changing goals, and bad management decisions.
I've been a 10x engineer at times. But I know I've also been a 0.5x engineer. The knowledge on how to solve a problem and how to find an answer doesn't change, but the perceived throughput of a person definitely does.