Mr. Yamaguchi is a middle-aged Japanese man who works as the president of EuroReptarLand. During Rugrats in Paris: The Movie, he was going to step down as the head of Yamaguchi Industries and had been looking for a replacement. Coco LaBouche was one of the employees under consideration, because she had made a lot of money for the company, but Yamaguchi was reluctant to name a replacement because he wanted the new president to be concerned with more than money--he wants to find a replacement who was good with children, since children are the main audience for the Reptar-franchise. When Coco lied and told him that she loved children and was engaged to a man with a child of his own, this seemed to delight him and he promised Coco that they would discuss the promotion after the wedding.
When he learned that Coco was deceiving him and that she actually hated children, he fired her on the spot. It's unknown who he ended up choosing as his replacement as head of Yamaguchi Industries.
Mr. Yamaguchi first physically appeared in Rugrats in Paris. He had been mentioned numerous times before that, usually by Charlotte, who holds him in very high regard. Sometimes he is described as being part of MegaCorp, other times he is head of a different company that Charlotte wishes to merge Megacorp with. He is an older man, probably in his late 50's or early 60's, given his baldness, dark gray hair and wrinkles. He wears glasses and has a small, thin mustache.
During his video conference with Coco, he is wearing a dark formal suit with a white handkerchief folded up in his pocket. When he attends the wedding, he is seen wearing a men's kimono, geta and tabi.
- The Rugrats occasionally have trouble pronouncing his name, referring to him as 'Mr. Yummy-Guchi' and sometimes 'Mr. Yummy-Sushi'.
- In the episode Chicken Pops, it's mentioned that he's attending Charlotte's company picnic, and Charlotte tells her assistant, Jonathan (over the phone), to make sure that the Japanese translator explains everything very carefully to Mr. Yamaguchi, because the previous year, Mr. Yamaguchi dunked his head into the coleslaw due to a misunderstanding. In Rugrats in Paris, however, he's shown speaking perfect English, suggesting that he learned it after the events of the episode.
- Mr. Hasagawa, an associate of Yamaguchi's, appears in the episode Miss Manners. Mr. Hasawaga shares Mr. Yamaguchi's love of children and family.
- "Yamaguchi" means "Mountain Mouth" in Japanese.
- In Rugrats in Paris, Yamaguchi was voiced by the late Japanese-American actor Makoto Iwamatsu, better known simply as Mako, who was known for voicing Iroh from Avatar: The Last Airbender (another Nickelodeon show) and Aku, the main antagonist of Samurai Jack.
You can find Mr. Yamaguchi gallery here.