From Bulbapedia, the community-driven Pokémon encyclopedia.
Ken Sugimori in September, 2010
Ken Sugimori (Japanese: 杉森 建, born January 27, 1966) is a friend of Satoshi Tajiri and illustrator of the original artwork for Pokémon games. He also has developed conceptual artwork for the movies, and illustrates TCG cards and merchandising.
Sugimori's change of style over the years has been noticeable. Initially, he used a stiff, lightly shaded style that was very reminiscent of the early works of Akira Toriyama. However, in recent years, his drawings of people and creatures have had more muscle definition, shading, and more natural and fluid poses.
The character in the Pokémon anime, Kenji (called Tracey Sketchit in the dub), may be an homage to him, especially as both enjoy creating art. This is similar to the way Satoshi (called Ash Ketchum in the dub) is named after Satoshi Tajiri.
Note: This list is very bare and is missing many credits.
Trading Card Game
For a list of cards illustrated by Ken Sugimori, go here.