Luigi is a character and an ally and life long friend to Yoshi. Yoshi likes it when Luigi rides on him. In Super Mario World 2: Yoshi's Island, the Yoshis have to save Luigi as a baby. He is Mario's younger, taller, thiner brother. In a way, he looks like his brother but wears different colours and has a neater moustache.
Luigi is portrayed as timid and a bit of a coward. He is know for his fear of ghosts but will reconsider at the thought of any monsters or trials.