Luigi is a major character in the Yoshi series, ally and lifelong friend to Yoshi and younger twin brother of Mario. 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 taller than his brother and thinner. 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 known for his fear of ghosts, but will reconsider at the thought of any monsters or trials.
He is the secondary protagonist of the Mario series.