Marvin Finister is Chaz's father, Chuckie and Kimi'sgrandfather, 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 Chaz and is a rugged outdoorsman type, and is in excellent shape. He tried to toughen and militarize Chaz when he was young, but failed. Marvin refers to the Rugrats as Pollywogs. While he loves Chaz and Chuckie, he and Shirley both regret not having more children to love.
Unlike most of the other grandparents in the series, Marvin and his wife are much younger and are still in their fifties. 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 colour hair.