Ralph is a grey adult male glasses wearing mouse who wears a green business suit with a green button down collared jacket and green dress pants and a white collared shirt, dark grey necktie, gold necktie clip, and a folded light blue hankie in his pocket, and black dress shoes.
Ralph Stilton is an anthropomorphic mouse who plays a minor role in season 3. He is the boyfriend of Princess Carolyn, and runs a greeting card company. His family owns Stilton Hotels (Most likely a play on Hilton Hotels), which provides him with free residency when traveling. Ralph seems to be mild-mannered and thoughtful, based on what we've seen of him.
Ralph appears to be very fond of cheese, eating at least two plates of it in That Went Well.
Ralph's last name, Stilton, is a type of cheese.
Ralph is homonymous with a popular 60s and 70s children's book character, Ralph S. Mouse, who was created by writer Beverly Clearly and popularized through a series of books starting with "The mouse and the motorcycle".
Ralph also bears great resemblence to a character named Geronimo Stilton, protagonist of a series of children's books by the same name which was written by Elisabetta Dami. They share the same last name, species, and dress similarly in a green coat and round glasses.
He is dating Princess Carolyn, she had time off one night, and asked Judah Mannowdog to arrange three dates for her, he did so, and Ralph was the only one she actually liked, despite him being a mouse. They ended up going out anyway.
In The Judge, he presents Princess Carolyn to his family who have a great dislike for cats. He can't help but join in on their racist traditions, but defends Princess Carolyn. It is implied the Stiltons suspect Princess Carolyn is pregnant and try in various ways to terminate her pregnancy. Ralph and Princess Carolyn later break up in Ruthie.