Luigi Cap

Luigi's Cap has been a key symbol for the Super Mario Bros. franchise. Luigi has had his hat in hand for his every appearance with no exceptions. Luigi has worn the hat since he was a baby.

History
Luigi's hat was meant to contradict Mario's red hat. Green is the Negative Color of Red. The hat was made green with a green "L" emblem. It has stayed that way ever since.

During the events of Super Mario Bros. 2, the tip of the cap had been changed to Black instead of his usual green, this happened for Mario as well.

Importance
In Super Mario 64 DS Luigi's hat was used to shape-shift into Luigi if the player was either Mario, Wario, or Yoshi. In the same game, Luigi is effected the same way as Mario and Wario if their hats are lost. Luigi's defense and attack sharply decline while his hat is absent from his head. If the player gets the hat back, Luigi's attack and defense revert back to normal.

Trivia

 * Luigi is seen without his cap is in Luigi's Mansion when he gets hit by a bomb or fire. If this happens, he will take off his hat and shake it because it's on fire, thus, he is seen hatless. Another time where he has no hat on is in New Super Mario Bros. when playing as Luigi, after a non-castle level is completed, he takes of his hat. The same goes for Mario.
 * Luigi's Cap is an item in Nintendogs that the players dog can wear.