Sora
Sora is the main character of Kingdom Hearts 2. He is the wielder of the Keyblade, a powerful weapon that can save the worlds, and conversely, destroy them when in the wrong hands. Sora is a very skilled warrior, as he can off many enemies with relative ease, and he can also use magic, though at the beginning his abilities in both fighting and magic are relatively weak, due to his sleep in a pod in the basement of the Haunted Mansion in Twilight Town. He gains new clothing through the three witches in Yen Sid's castle, clothing which allows Sora to transform into new Drive Forms, such as Valor, Wisdom, Master, Final, and Anti-Sora. It also allows him to use Magic without hesitation, as it pulls magic from his surroundings and recharges his Magic. Sora is a loyal friend to anyone he cares about, and will not back down from helping them out.
Donald Duck
One of Sora's best friends. He and Goofy are searching for king Mickey after he left the castle, and assisting Sora. Donald is the court magician of Disney Castle, and as such, is the most powerful magic wielder in your group (at least until Sora levels up magic all the way). He wields a magic staff, and has a hot temper, but can (and will) prove useful in battles against multiple enemies and bosses.
Goofy
One of Sora's best friends. He also is looking for the King, and helps Sora. He is the Captain of the Royal Guard at Disney Castle, and carries a shield. As such, he does have the highest defense and health of the group (At Least until Sora Levels up completely) and is a specialist with special attacks. Because of the variety of special attacks in Goofy's arsenal, combined with his normal attacks, Goofy is a great overall ally to have in any battle.
Kairi
She is Sora's close friend (and possible love interest). She doesn't fight very often, but later on, she actually fights with a Keyblade! You can't control her, but it is pretty awesome to see her fight. She is a good friend to Sora.
Riku
He is one of Sora's best friends. He is also Sora's rival. He is fairly strong, and also is an extremely good ally to have, due to the fact he has a shield and ranged reaction commands. He also has one of the most powerful Limit Breaks in the game, and you get to control him for a few seconds, during the last battle. Very strong warrior, he also wields the Keyblade, in the form of the Gullwing. He is only second to Sora (and Roxas) in terms of battle skills.
Diz
Maleficent
King Mickey
The King of Disney Castle. He is an elusive character in the storyline, but is an important one....He IS the King (duh!). That being said, he TOO wields the KEYBLADE (my gosh, how many Keyblades are there! [The most powerful one belongs to Sora though]). His Keyblade is a golden version of the Kingdom Key, and, even though he is the king, he possesses the least powerful Keyblade. He can only be controlled in certain instances during certain battles when you get knocked out. Although awesome to play as Mickey, he is weak, but is fast, so its a different battle style than anything you will use....just don’t count on getting to play as him if you don't want to risk dying!
Xemnas
Roxas
He's the Nobody form of Sora. He is Organization XIII's number XIII. That being said, he wields the keyblade, just like Sora. He is also the first character in the game to use the dual keyblades. Amazingly, Roxas pulls this off without the use of drive forms, but you only get to use two keyblades as Roxas when you fight Axel...and that is one hell of a match!!! He is just as powerful as Sora (His level gets transferred to Sora), although he lacks the support of a party and the skills to heal and attack using magic.