I should mention that the cover artist was Jim Jiminez of Atlantis Studios. He did the covers for books 2 and 3, as well.
The original basic character concepts/designs came from me and from my sometimes-writing partner, Bobby Politte, and were first rendered visually by Kevin Phillips, Tony Perna, and Rob Davis.
Other artists have elaborated on their looks, including Chris Kohler , Danny Wall, Mark Maddox, Jeremy Haun, Robin Sevakis, and (last but certainly not least) Mitch Foust.