Here's the author's page: http://www.alexhorleyart.com/home.html

He also created official Illidan artwork (both regular & 1k wins portraits) for Ashes of Outland, as well as a few other card arts (e.g. Kargath, Metamorphosis). Well, to be honest, he makes a few card artworks for basically every expansion :) He also did a bunch of official artworks for other Blizz games.

I really dig his style!