Sora has a typical brave and heroic personality, meaning he'll willingly risk his life for people he doesn't even know. He's extremely loyal to his friends, and has shown to be extremely forgiving to Riku (even forgiving Riku for the times he's tried to kill him). He constantly "thinks positive" and is therefore highly optimistic.
Sora appears to be a natural swordsman, most likely due to all his training against his friends on Destiny Islands. His skill with the Keyblade increased greatly over his journey, and he has become a Keyblade Master.
Sora wields his Keyblade with a two-handed style, with both of his hands on the handle during his initial strikes, although he often finishes with one handed swings. While Roxas and Riku rely on speed and quickness, Sora is more of a "heavy hitter". He uses strong swings and slashes and powerful finishes to damage his enemies, and repeatedly attacks until his opponent succumbs. But, this is not to say Sora isn't fast, as he can quickly dash through enemies. Like his Nobody, Sora also wields the element of Light as a weapon, but not to the extent and level that Roxas can. He can use light to augment his Keyblade swings during combos, and can finish attacks with bursts of light that encircle him. This ability is called Explosion.
Sora is also well-versed in various magic spells, even more so after training with Merlin. In Kingdom Hearts II, his basic combo is much stronger and he gains the Drive Form ability after obtaining new clothes, which give him even more mastery over his strengths. In addition to the abilities that each form grants him, Sora's speed and strength are also increased.
Donald Duck, in Disney canon, is a sailor with a dangerously short temper. In Kingdom Hearts, Donald is the Royal Magician of Disney Castle, presided over by King Mickey. He isn't very smart overall, and often provides comic relief more than advancing the plot despite the amount of time he appears in the series. Despite his rash and aggressive personality, he is loyal to his friends.
Though he initially only cares about Sora as a means to track down King Mickey, Donald soon grows to deeply care for him as a friend.
Goofy is Captain of King Mickey's army. He and Disney Castle's court magician Donald went out to search for the King, and ended up teaming with Sora for the rest of their journey.
Despite his position at Disney Castle, Goofy dislikes using weapons (instead using a simple shield in combat) and attempts to avoid fighting whenever possible, preferring to find peaceful solutions to problems. Though simple-minded and clumsy as always, and constantly the butt of comic relief, Goofy is the constant voice of optimism and, surprisingly, selectively perceptive, often noticing things others miss and keeping his cool when Sora and Donald lose it. He comes off as the sage of the group, despite how he is portrayed in the Disney cartoons.
Kairi is caring and kindhearted, not afraid to speak out her mind. However, she is determined and courageous when someone she cares about is in danger, often risking her own safety to help that person. She also makes friends easily, quickly befriending Hayner, Pence, and Olette in Twilight Town. In contrast to Sora and Riku, who were both bothered by not knowing about Kairi's hometown, she took it in stride and was able to look at the positives about living in the Destiny Islands. She is loyal and headstrong, as well as stubborn to a point.
Because Kairi is a Princess of Heart, her heart possesses no darkness within it, leading to the unique birth of Naminé when she accidentally gives it to Sora and he sacrifices himself to restore her heart. Like the other princesses, she has the power to open the Final Keyhole to Kingdom Hearts in Hollow Bastion once she is gathered with the rest of the princesses. Kairi also appears to have some kind of latent magical ability, as seen when she manages to restore Sora's humanity after he becomes a Heartless. Since the other Princesses of Heart possess the abilities to hold back darkness and upgrade other people's powers, it is no doubt that Kairi can do so as well. Kairi's abilities in combat are limited. She does, however, have the rare ability to wield a Keyblade.
In Kingdom Hearts, Riku is a calm, cool, collected (and not to mention cocky) teen who is not afraid to go far beyond his limits. This shows through when he shows no fear in stepping into the dark portal when Destiny Islands was being consumed by darkness, along with his statement "I'm not afraid of the darkness!"
He also showed a strong competitive streak, along with a bit of jealousy. He shows his competitive side when he challenges Sora, saying that his heart is stronger than Sora's heart. It is not actually said aloud, but thanks to Maleficent, he became increasingly jealous of Sora. It started with him finding out about Sora's new friends, and his thinking that he had been replaced. The jealousy grew when he learned about Sora possessing the Keyblade. The jealousy turned into rage, resulting in the battles against Sora throughout KHI, and his possession by Xehanort's Heartless.
Though his traits were not too favorable in KHI, he becomes more heroic in Chain of Memories. Riku has many realizations. One of these realizations was that he let his heart become weak. From that moment on, he began to shy away from the darkness in his heart. Through the scores of fights and battles in Castle Oblivion, he makes another big realization: he can't get rid of the darkness in his heart, and decides to use it without turning from the light like before. He matured immensely, and along with leaving his past behind him, he also left a lot of his unfortunate traits.
In comparison to Sora's two-handed style and Roxas' dual-weaponry, Riku attacks with a fast one-handed style with his Soul Eater/Way to the Dawn. Riku attacks very quickly with either weapon in combat, and is just as able with his weapons as Sora is with his. His strength and agility are best demonstrated on Destiny Islands, where he is known as the strongest child on the island (Tidus remarked that he, Wakka, and Selphie were defeated by him even after they triple-teamed him), and possesses an athletic springing kick if knocked down. Riku's other main form of attack is Dark Aura, in which he fires multiple blue fireballs of dark energy. Though Sora has bested Riku on several occasions, it is still unclear whom is stronger.
DiZ is a mysterious man whose face is concealed with bandages. He seems to have a specific mission for vengeance in mind, and begins going about it by attempting to rejoin Roxas with Sora, essentially restoring the rest of Sora's memories and awakening him from his year-long sleep.
Maleficent is a witch who made her debut in Sleeping Beauty (1959). In Kingdom Hearts, she led a band of Disney villains to capture the Princesses of Heart and devour the hearts of all worlds, but her plans were thwarted in a confrontation with Sora, Donald, and Goofy, ultimately falling to them in her powerful dragon form. However, despite her apparent death, she makes a return in Kingdom Hearts II in an attempt to once again control the Heartless and take all worlds. This time, she has a loyal lackey in the form of Pete, the rival of Mickey Mouse.
The King of Disney Castle. He is an elusive character throughout the storyline, but is an important one, being the King. He too wields the Keyblade. His Keyblade is a golden version of the Kingdom Key called the Kingdom Key D. In truth, the source of this mysterious Keyblade is darkness, as opposed to the light version Sora wields. In Kingdom Hearts II, he can be controlled in certain instances during certain battles after Sora has been knocked out. Mickey isn't as strong as Sora, but he is fast, giving you access to a new battle style. When playing as Mickey, you can either revive Sora with full health by filling the drive gauge with the reaction command, or simply fight the boss until Mickey loses all of his HP to restore only a small percentage of Sora's.
Xemnas, as the superior, is the first member and founder of Organization XIII, with all other Nobodies under his control. He is the most powerful member, so much so that Marluxia would not dare to face him, even with the support of Axel and Larxene, until Sora was completely under his control. Furthermore, Vexen immediately complied with Marluxia's order to eliminate Sora when he made the empty threat that he would report Vexen's failure to the superior. He also appears to be the Organization's most intelligent member.
Being the founder of Organization XIII and apparently the oldest of Nobodies, Xemnas is truly emotionless and does not even remember what it was like to have emotions. He claims that this allows him to have a clear understanding of the heart, but in reality this has warped his mind into believing that only anger, hatred, and other negative feelings make up a heart.
His lack of emotion gives him absolutely zero remorse over his actions, as well as the loss of the other members of the Organization. The only thing he truly cares about is Kingdom Hearts and his desire for power, and even laments it when it is damaged. Unlike the other members of the organization, Xemnas does not seem to want Kingdom Hearts for a true existence. Rather, much like his Heartless counterpart, he wants it to use it to obtain power. This concept is furthered as Xemnas thinks that nothingness is the source of much power and does not seem to despise it in the slightest.
Roxas, unlike other Nobodies, seems to possess real emotions, stemming from the fact that he, like Naminé, is a special Nobody.
When he attacks with his full power, Roxas dual wields two Keyblades and uses the element of Light, becoming a highly dangerous foe. He can glide at fast speeds, so fast in fact that he leaves behind a lens flare, and control thirteen sword-shaped shields of light energy which can connect to form a laser array. He can levitate his Keyblades in the air and whirl and spin them rapidly, showing a great deal of proficiency and skill with the blades, and can also counter any extended combo with a more powerful one of his own, even creating a ring of damage just by twirling them in a circle. His special attack involves him floating in the air and shooting his thirteen light shields around the arena, which then light it up in a thick twilight mist as Roxas begins shooting blue spheres of light at his opponent from energy gathered in his hands. He'll often attack rapidly from side-to-side, confusing the opponent, leaving a trail of light behind him. He can also perform the Duel Bout technique (similar to his Samurai Nobodies) where he rushes at his opponent and slashes at them quicker than the blink of an eye, causing intense damage if not repelled. The twist is that Sora can utilize Roxas' Keyblades if he does repel the attack. However, when Sora steals Roxas' Keyblades, Roxas resorts to utilizing his light shields to full effect, before moving in to steal his Keyblades back from Sora.
In comparison to Sora, Roxas seems to have a far more aggressive style: he is constantly on the offensive, and abandons any defensive moves he had previously used, such as the Guard technique, in favor of speed and strength. This makes it easier to catch him off guard (since he is never on guard anyway) but it can still be tough to hit him since he is so fast. In their mental struggle in The World That Never Was, he briefly manages to overpower and disarm Sora.
In Kingdom Hearts II: Final Mix, after you have defeated Roxas, you obtain a special Keyblade modeled after himself, the Two Become One Keyblade.
Naminé is a different type of nobody, not only due to the fact she seems to process emotion, but also because she was born from Kairi's heart. The body and soul needed to be reborn as a Nobody belong to Sora. Naminé has no memory of her former life, but due to the fact that she used Sora's body and soul, she can manipulate his memories and those whose hearts are connected to his. Naminé has had a very cruel history, with Larxene, an Organization member, having physically and mentally abused her. She was also locked in a room by herself where Diz would threaten her and call her a witch during the time she was fixing Sora's memories. Naminé is also willing to risk her life to help people who are being deceived or are in need of help. She broke into the Organization stronghold to get Kairi and Pluto out and was willing to forgo her existence as an independent entity to make Kairi whole again.
Pete is a character new to the series, introduced as an ally of Maleficent. He originates from Steamboat Willie (1928) as a rival to Mickey Mouse (in what was also Mickey's first appearance), and seems to play the same role here, as Goofy and Donald recognize him. Unlike Maleficent, Pete is clumsy and generally finds himself at the butt of jokes. Still, he is extremely loyal and can be found in many worlds on missions to control them with Heartless.