Luigi is Mario's brother and is acted by Christopher Anthony Muller. He is an important character and first appeared in Episode 1, and has appeared in almost every episode after that. He doesn't have a mustache because he is supposed to be a younger version of the popular Nintendo character.
Luigi is an important character in the series, and first appeared in Episode 1. He plays a big role in the plot, and has appeared in almost every episode. He tags alone with Mario, (with only occasional fights) and helps him through his journey.
Luigi also has an important part in the movie. He has an alter-ego, Mr. L, after being consumed by Nox Decious. Shortly after, though, Mario rescues Luigi from this dark state. He also fights Bowser's servant, Kamek, while Mario fights Bowser himself.