 
The Skull Kid is a character first seen in Ocarina of Time. There are a few of them that can be found in the Lost Woods, a maze-like forest near the starting location of the game. He appears separated from the other Skull Kids. In the direct sequel to Ocarina of Time, Majora's Mask, the Skull Kid that Link befriended in Ocarina of Time is the same as the main antagonist in the storyline. He was somewhat of a bully and always played tricks, hence he could never make any friends. Four of his closest friends, the Four Giants of Termina, also got angry at him for this reason. He believed when they left Clock Town to live with their races that they were leaving him behind. Not long thereafter, he was taking shelter from the pouring rain, all alone and very unhappy when he met Tatl and Tael and was quickly befriended by them. He continued to play tricks, including on a man called the Happy Mask Salesman, who has a mask called the Majora's Mask in his possession, which Skull Kid takes. Under its influence and with the help of the mask's power, he cursed many people in Termina as well as Link, sealed away the Four Giants into evil masks and cursed the moon, forcing it to abandon its orbit and crash into Termina, threatening to annihilate its inhabitants. At the end, the Skull Kid notes that Link "smells a lot like that fairy kid who taught me that song in the woods," revealing that this is the same Skull Kid that Link befriended via "Saria's Song" to get a Piece of Heart.
A Skull Kid also makes an appearance in Twilight Princess. He also has the ability to open doors in the Sacred Grove, to guide the player to the Master Sword and the temple of time. He also appears in The Legend of Zelda manga.