Luigi

Luigi is best described as the "underdog" of the Mario Bros., often going unnoticed due to his reluctant nature. He is often slightly cowardly and is terrified of ghosts according to his diary. Nevertheless, Luigi musters his courage for a couple of adventures in the Paper Mario series, showing bravery and determination when it is needed. Luigi is generally easygoing and is very kind and considerate to those around him. He is certainly jealous of Mario's success; however, he does not let that jealousy get in the way of their good relationship. It is revealed at the end of Paper Mario that he wishes that he could sleep on the top bunk. 

In The Thousand-Year Door, he is shown to be arrogant and somewhat of a liar, slightly exaggerating his stories to make himself look more heroic. Some of his partners show incredible disdain for Luigi and some of them, like Blooey the Blooper, only stick around because he owed them a debt.