The term 'BROTHER OF NINTENDO'S MARIO' is solved by the 5-letter word 'LUIGI'. Luigi is a fictional character featured in video games and related media released by Nintendo. He is the younger brother of Nintendo's mascot, Mario, and first appeared in 1983 as the protagonist of the game Mario Bros. Luigi has since appeared in many other games throughout the Mario franchise, including Super Mario Bros., Super Mario 64, and Mario Kart.