Marvin Finster

Marvin Finister (voiced by Stacy Keach and Corey Burton) is Chas' father, Chuckie and Kimi's grandfather, and Shirley Finster's husband. For the most part, he is very old-fashioned and conservative. This is made evident by his lack of knowledge about the Dr. Lipschitz method of child-raising, his question about using "rabbit ears" to watch TV, and ignorance on the subjects of cable or text messaging. He is the opposite of Chas and is a rugged outdoorsman type, and is in excellent shape. He tried to toughen and militarize Chas when he was young, but failed. Marvin refers to the Rugrats as Pollywogs. While he loves Chas and Chuckie, he and Shirley both regret not having more children to love.

Both Marvin and Shirley are ecstatic when both Kira and Kimi join their family, saying "Now we got two grandkids."

Unlike most of the other grandparents in the series, Marvin and Shirley appear to be significantly younger and are confirmed to still be in their fifties (they were most likely in their 20s or 30s when they had Chas). As a result, Marvin has a more fit appearance as well as dark hair that is still transitioning to gray. In Rugrats in Paris, he seemed to have orange colored hair.