Marshal Mouse is an anthropomorphic mouse. He was presumably the husband of Matilda Mouse and became the father to several children, with his progeny likely including the likes of Marcus Mouse, Milton Mouse, and Mortimer Mouse. He may have been a man of wealth, as a picture of him showed him with a large jewel on his finger and wearing a fancy suit.
Marshal is an anthropomorphic mouse with dark hair leading down to his shoulders and thick eyebrows. He wore glasses and was pictured holding a bowler hat, indicating he was fond of wearing them.
Behind the Scenes
Marshal Mouse appeared in Mr Slicker and the Egg Robbers in photograph form. A picture of him was on a page in a Mouse family album. The same page had pictures of Matilda Mouse, Milton Mouse, and Milton's family, indicating that they were all from the same branch of the Mouse family. Based on his last name and the fact that he is explicitly stated to be Minnie's "grandpa", it is very likely that he is the father of Marcus Mouse.