Leon is a supporting character in the Kingdom Hearts series and leader of both the Heartless Resistance and the Hollow Bastion Restoration Committee. Originally he went by the name Squall Leonhart, but due to his world being destroyed by the Heartless, he changed his name in an attempt to amend for his mistakes. Leon is twenty-five years old at the beginning of Kingdom Hearts and Kingdom Hearts: Chain of Memories and twenty-six during the events of Kingdom Hearts II.
Squall was the main character of Final Fantasy VIII, in which he wields the notorious Gunblade.
Leon, along with Cloud, Aerith, Tifa, Yuffie, and Cid were originally set to appear in Kingdom Hearts Birth by Sleep. But in the final release they were removed from the game because, according to Nomura, there were already too many plot lines, and it would have become confusing.
Also, Tetsuya Nomura has stated in an interview that the main reason he had Squall change his name to "Leon" was in order to avoid spoiling the revelation of Squall's big role in Mickey's first letter to Donald. Also, Leon is shown to have the wings of Rinoa Heartilly, his lover from Final Fantasy VIII, on the back of his jacket, implying that something which specifically happened to her was a major factor in Leon changing his name.
 Between Kingdom Hearts Birth by Sleep and Kingdom Hearts
Squall Leonhart grew up in the paradise world of Radiant Garden until it was consumed by darkness. Ashamed and angry that he was unable to defend his home and his loved ones from the Heartless, Squall assumed the name of "Leon" in order to distance himself from his past, vowing never to use his real name until the Heartless are defeated and his world restored.
Leon awakened in Traverse Town along with the few fellow Radiant Garden refugees Yuffie, Aerith, and Cid, none of whom changed their names as Leon did. During his teenage years, Leon led the fight against the Heartless, effectively keeping an area of Traverse Town safe against Maleficent and the growing tide of Heartless. He was also known to travel between worlds in his Gummi Ship, assisting other refugees in peril and relocating them to Traverse Town. His actions did not go unnoticed, eventually gaining the attention and confidence of King Mickey, who was watching the growing battle warily.
 Kingdom Hearts
Nine years after the fall of Radiant Garden, now named Hollow Bastion, when the wielder of the Keyblade was revealed, King Mickey ordered Goofy and Donald Duck to find Leon, trusting that Leon would inform them of the circumstance and help them find the wielder, Sora. It turned out, however, that Leon had already found Sora within the safe First District of Traverse Town, challenging and either defeating the boy in a duel or being defeated before dragging Sora back to the resistance's hideout; a room in one of Traverse Town's motels. There, Leon and Yuffie explained to Sora about the Heartless and his destiny as the Keyblade's chosen one. Uniting Sora with the newly arrived Donald and Goofy, Leon then sent them on their way.
When Sora, Donald, and Goofy returned to Traverse Town again seeking Leon's help, they find him in the Secret Waterway, underneath Merlin's house, training. Here he offers information about the Keyholes of each world that lead to the heart of the world. He explains that the Heartless are drawn to the heart's power and would corrupt it, thus causing the world to disappear. This is why Sora's Keyblade is so important, because it has the power to seal them from the Heartless.
After escaping from Hollow Bastion, Sora, Donald, Goofy, and Kairi sought shelter with Leon's group in Traverse Town. Sora informed Leon of everything that had happened, prompting him to follow Sora and company when they left for the final battle with Maleficent in Hollow Bastion.
After Sora defeats the Behemoth Heartless that guards Hollow Bastion's Keyhole, Leon stands waiting to bid his farewells, for after Sora seals the heart of all worlds, Kingdom Hearts, the two groups might never see each other again.
Later, Leon, Yuffie, and Aerith can be seen wandering the Hollow Bastion Library, reading the books.
After Sora sealed Kingdom Hearts and returned the universe to its order, Leon, Yuffie, and Aerith are reunited with Cid and Cloud in Hollow Bastion.
 Kingdom Hearts: Chain of Memories
After the defeat of Ansem, while skirmishing through Castle Oblivion, Sora, Donald, and Goofy later meet Leon and his friends in a memory-based version of Traverse Town. However, like the town itself, little did Sora and his party realize that Leon and his friends were actually the product of Sora's memories that were being manipulated by Naminé. Due to that, the Leon and his friends that Sora encounter have no memories of ever meeting Sora, but somehow know his name, which they could not explain how. Like the Leon from the first game, he nonetheless decides to help Sora and company, such as by teaching Sora the card-based system as well as providing the Simba and the Key of Guidance cards in order for Sora to proceed. Before Sora leaves, Leon ensures him that he will be okay; no matter what shape reality takes, and that while he may not remember Sora, he knows that he is in his heart.
 Between Kingdom Hearts: Chain of Memories and Kingdom Hearts II
After the lost parts of Radiant Garden were liberated from the End of the World, Leon and his friends formed the Hollow Bastion Restoration Committee to restore their world to its former glory. During the course of their work, they rebuilt much of the town and began reconstruction of Ansem the Wise's castle, removing much of the modified machinery that was added to it. Also, due to Naminé tampering with Sora's memory, Leon lost his memories of his former friend.
 Kingdom Hearts II
By the time Sora makes his return to Hollow Bastion, Leon's memories had returned. Leon explains to Sora that they've been having problems with the Heartless as of late. The Organization appears and forces Leon and Sora to battle several Nobodies.
During the Battle of the 1000 Heartless, he, along with the rest of the Committee, helps Sora fight the Heartless on the Ravine Trail. He and Cloud were also shown back to back and surrounded by Heartless, bantering briefly before charging at their enemies. The two later returned to Hollow Bastion's outer wall and witnessed Sora's escape at the end of the battle.
By the time they visit again, the town is infested with Heartless from Space Paranoids. While Sora, Donald, and Goofy set off to Space Paranoids to help Tron, Leon goes to pick up the eradicator program that Cid has been working on to defeat the Master Control Program for good. They eventually succeed, and Tron is able to remind everyone of the town's true name; Radiant Garden.
After Sora and Riku return to Destiny Islands, he is seen in Merlin's house, reading a letter that produces a strange glowing butterfly shape that floats towards the ceiling and then vanishes.
 Kingdom Hearts Re:coded
After Data-Sora collects every Ending Card in Castle Oblivion, Data-Roxas allows him to open the final door and learn the truth behind the hurt. Right as Data-Sora moves to open the door, illusions of Leon and Yuffie appear to congratulate him for keeping Traverse Town safe, explaining that something urgent came up that they had to deal with. They express a wish to someday work alongside him, and give him a Debug Device: Y and a Heat Sink Belt before departing.
In Kingdom Hearts, Leon's appearance is similar to his original appearance in Final Fantasy VIII, but with several differences. He bears some resemblance to Tetsuya Nomura's original design for Squall Leonhart, sporting long, brown hair as opposed to the short hair he had in his original game. Leon retains the black gloves, black, zipper-lined shoes, a silver Griever necklace, and a white undershirt that his Final Fantasy VIII incarnation had, and his short, black jacket is similar. Leon's jacket, however, lacks the fur collar, is short-sleeved, whereas Squall's sleeves were quite baggy, bears red wings on the back, presumably similar to Rinoa's duster, and has a red Griever symbol on each shoulder.
Leon wears three brown belts on his left forearm and has three buckles on his right thigh, while he wore three black belts on his left thigh in Final Fantasy VIII. Leon's black pants also sport a vertical zipper going down the side of each leg. Leon wears two brown belts and two black ones around his hips, all of which are quite loose except for one, a black one worn properly around his waist. In Final Fantasy VIII, he only wore two brown belts. His eyes are blue and he bears his distinctive scar, which runs diagonally across the bridge of his nose.
In Kingdom Hearts II, Leon's appearance changes slightly to match his original appearance more. His hair becomes a lighter shade of brown and shorter, and his bangs sweep to the left side of his face in the same manner as his hair in Final Fantasy VIII. He also adds the white fur collar to his jacket that was absent in Kingdom Hearts.
In both of his appearances, Leon wields his silver "Revolver" model Gunblade, complete with the Griever keychain.
When Sora first meets Leon, his personality is that of a withdrawn and quiet loner. Eventually, he opens up to become a more caring person, as seen as when he is worrying about Sora, Donald, and Goofy's safety in the aftermath of the Battle of the 1000 Heartless. Although appearing as sullen and brooding in Kingdom Hearts, after returning home to Hollow Bastion in Kingdom Hearts II he seems to be more cheerful, is seen to be smiling more often, and also has a friendly rivalry with Cloud. Leon has also good leadership qualities which he displays throughout both games, mirroring the character development of the original Squall Leonhart of Final Fantasy VIII, who himself began as a brooding and unconcerned loner but eventually became a caring friend and leader thanks to his friends. Leon also stands out from the other Final Fantasy characters in the series. For example, Leon leads the Hollow Bastion Restoration Committee and is the only Final Fantasy character in the group to have originated in Final Fantasy VIII.
Leon may be mild-mannered outside of battle, but all gloves are off when faced with a tough opponent. Utilizing his Gunblade to deal massive damage with various cutting combos, he wields the element of fire to some degree, able to shoot Firaga spells. When his HP dwindles, he uses a desperation attack that causes his Gunblade to enlarge drastically, which allows him to deal much more damage.
Leon originated as Squall Leonhart, the main protagonist in Final Fantasy VIII. He is studying to become a full-fledged member of the mercenary force known as SeeD, and specializes in the Gunblade, one of only two current cadets to do so. Ordinarily introverted to the point of seeming rude to others, he is forced to take a role of leadership as the world moves toward conflict, similar to his taking on leadership of the Final Fantasy characters in Kingdom Hearts after the fall of Radiant Garden. His scar still remains slashed across his face just as it did in Final Fantasy VIII, but he is unaware of Seifer in Twilight Town.
"Leon" shares his pseudonym with the English name of the Final Fantasy II character Leon, whose original Japanese name is shared with Squall's surname, Leonhart.