The term 'MIGHTY DOG RIVAL' is a crossword solution that can be filled in with the brand name ALPO, which is a four-letter word. ALPO is a brand of pet food that has been around since 1936 and is owned by the Nestle Purina PetCare Company. It is a popular choice for dog owners and is known for its high-quality ingredients. ALPO is a major competitor to other brands of dog food, such as Mighty Dog, making it a fitting answer to the crossword clue.