Sora
A boy of 14, Sora is on a quest to find his friends Riku and Kairi, while completing his duties as Keyblade Master.
Donald
Court Mage of Disney castle, Donald is a friend of not only Sora and Goofy, but of the king. Donald in this game doesn't participate in battle like the original game, but instead appears as a "Friend Card" throughout the game in battle, casting spells to help Sora.
Goofy
Head of the Knights of Disney Castle, Goofy uses a shield instead of a sword or mace. Goofy in this game doesn't participate in battle like the original game, but instead appears as a "Friend Card" throughout the game in battle, using his shield as a weapon in various ways.
Riku
After leaving Sora and Kairi outside of Kingdom Hearts, Riku has come to Castle Oblivion to find his friends. Riku is a year older than Sora, and slightly more powerful, but calls upon the power of Darkness throughout the game instead of magic.
King Mickey
The king who reigns over Disney Castle. He set off alone to protect his world and all worlds from the dominion of the dark. When Riku fell into the realm of darkness, the king showed him the way, but the two were separated when the door to darkness was closed.
DiZ
DiZ is a strange fellow, not revealing much throughout the game. He and the King apparently have met, but nothing is certain.
Naminé
A strange girl who apparently has some connection to Sora and Riku. She is being controlled by the Organization.
Organization Members
The Organization is a shady bunch of people who are currently trying to use Castle Oblivion for some devious purpose. There are apparently 13 members, but only 6 are named in this game. The leader is also mentioned, but not by name.
Vexen
No. 4 in the Organization One of the original Organization members, Vexen is a man of science. Using Riku as a test subject, Vexen has tried to control Sora many times. He wields an ice shield in battle, deflecting any frontal attacks. He is also in Riku's path.
Lexaeus
No. 5 in the Organization A born warrior, Lexaeus effortlessly brandishes a gigantic tomahawk. To counterbalance his rival Marluxia's bid for Sora's power, Lexaeus tried to conquer Riku. He failed, but with his dying strength dragged Riku into the realm of darkness. He appears only in Riku's path.
Zexion
No. 6 in the Organization Zexion generally avoids dirtying his own hands when there are deeds to be done. However, with the destruction of Vexen and Lexaeus, he was force into action. Zexion confronted Riku disguised as Sora. But Riku no longer feared the dark, and victory was beyond Zexion's reach. He appears only in Riku's path.
Axel
No. 8 in the Organization A mysterious figure who stands in Sora's path. Hard to read, half the time Axel seems to just be messing around... but for all we know, he's done more thinking than everyone else put together.
Marluxia
No. 11 in the Organization Wielding a scythe, Marluxia heads the group that rules Castle Oblivion. Wanting to take the power of the Organization for himself, he tries to obtain the power of the Keyblade by use of Naminé.
Larxene
No. 12 in the Organization As one of the few who rules Castle Oblivion, Larxene is in this for herself. Even though she is the only female of the Organization, she is not to be taken lightly with her speed and deadliness. She appears only in Sora's path.