Luigi Is Mario'S Younger, Taller, Thinner Twin Brother. He Is A Major Protagonist Of The Mario Series. Luigi Has Helped And Fought Alongside His Brother On Many Occasions. Throughout His Life, He Has Lived In Mario'S Shadow, Developing Both Cowardly And Heroic Tendencies. Mario Bros. Marks His First Appearance In The Mario Series And His Debut In General. Originally A Palette Swap Of Mario, Luigi Was Created To Facilitate A Second Player Option.