From Bulbapedia, the community-driven Pokémon encyclopedia.
Kouichi Ooyama (Japanese: 功一 大山) is one of the original game designers of the Pokémon Trading Card Game.
He made a cameo in Pokémon Card GB as a Pokémon Card researcher, Dr. Ooyama (Dr. Mason in the English version of the game). Dr. Ooyama looks like Ooyama, but with grey hair, a lab coat, and a Pokémon Card attached to his head.
In the TCG
Kouichi Ooyama has illustrated various things for the Trading Card Game. He illustrated the Ooyama's Pikachu Lv. ? card, being credited as "Ooyama." It features a drawing of Ooyama where the Pokédex entry usually is. He was credited as "Dr. Ooyama" for the illustration of the well-known "bilingual" Exeggutor card, which had its text printed in both English and Japanese. Like Ooyama's Pikachu, it features a drawing of the illustrator in place of the Pokédex entry, who is in this case "Dr. Ooyama."