Peter Lee is an artist at Blizzard, and is responsible for a large amount of the concept art so far released for Diablo III. Peter seems to specialize in landscapes and environmental art, but he draws a lot of monsters and characters as well.
His alias Dragoon, and he is one of the Blizzard artists who contribute to the Sons of the Storm art website.
His home page can be found here. (Currently down.)
Some of his work on Diablo III: