Wario Cap
Wario's Cap is Wario's most distinguishing piece of clothing. The hat is yellow with an exceptionally large blue "W" emblem inside a small white circle. The hat also features a white rim and has been featured in every Wario game (besides its excessive absences in the WarioWare series, for Wario scrapped his classic look and wore a biking outfit for that series).
History
Wario's hat was based fully on Mario's Cap with minor differences. The hat got its yellow color artwork from Super Mario Land 2: 6 Golden Coins but never got it colored that way in games until Wario's Woods for every game he appeared in up until that point were black and white Game Boy games. Like Mario, Wario has been seen wearing the cap since he was a baby as proved by Yoshi's Island DS.
In his profile picture after lose in Mario Kart 64 and Mario Kart: Super Circuit will show Wario biting his cap.
In Wario: Master of Disguise the hat plays a more important part as a checkpoint in each chapter. There are many hats scattered in each chapter and if the player found one they could save the game. By saving, the player wouldn't have to start from the beginning of the level if they died, but wherever the checkpoint hat was.
Wario's hat affects Wario as Mario's hat affects Mario. If Wario were to lose his hat at any time, most notably in Super Mario 64 DS, his defense and strength would sharply decline. By getting the hat back, Wario would have a steadier chance of survival in an extremely tough level. While his hat is absent, Wario would be unable to pick up any hats or turn metal. Also in that same game, Wario's Hat could be picked up by either Mario, Luigi, or Yoshi to shape-shift into Wario. Until he is unlocked, the only course his cap appears in Hazy Maze Cave. If he loses his cap and gains a star from another level, Wario can simply talk to Toad (who will find and be wearing Wario's cap). While the cap is important to Wario, Toad diminishes it by saying that it "reeks pretty bad" and that Wario should wash it out more often.
Colors & Variations
Wario's hat hasn't always been it's classic yellow. In some segments of Wario's Woods his hat appears purple and in Wario Land 3 Wario's hat is white. In Super Mario Land 2: 6 Golden Coins and Wario Land: Super Mario Land 3 his hat was gray due to lack of color on the Game Boy.
The hat has also been imitated on different headgear Wario has worn. Wario's WareWare helmet is in the style of his hat with the white rim and blue "W" emblem. Wario's Jungle Trek hat from Wario Land also has his signature blue "W" emblem.
