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 Cleary and popularized through a series of books starting with "The mouse and the motorcycle"