There are many who I admire, but I'll pick out 2:
1. Ansel Adams. I grew up in California and his photographs were the first that were imprinted in my mind and what first instilled in me the love for both photography and the outdoors. Although I have since discovered photographers whose work I like every bit as much, you never quite lose the special place you have in your heart for your "first".
2. Harold Edgerton. As an engineer, I have always wanted to explore what could be learned through photography. Edgerton really pioneered the world of technical photography. Although he didn't really create art the way Adams did, he created some incredible images and pioneered techniques that help to shape parts of our craft today.