Snow White

Snow White is an original character from the 1937 Disney animated movie, Snow White and the Seven Dwarfs. She is one of Princesses of Heart whose heart was required to open the final door

Kingdom Hearts
Snow White's world was destroyed by Maleficent. She was one of the first princesses to be captured and taken to Hollow Bastion.

In the game, if Sora seals the keyhole of Deep Jungle before sealing the one of Wonderland, Snow White is set to appear in front of the Disney villains instead of Alice.

When the darkness of the keyhole from Hollow Bastion spread throughout the world, Snow White and the other five princesses used their power to shield it inside in order to keep it from spreading throughout the universe.

When Kingdom Hearts was sealed she was returned to her own world.

Kingdom Hearts II
Although she did not appear in the game, Snow White's name was part of the password that allowed access to the DTD dataspace in Tron's world.

Birth By Sleep
Recently, a screenshot has been released confirming that there will be a Snow White world in Birth By Sleep, meaning that Snow White will almost certainly reappear.