- "What of the future? A free France where we all take care of each other?"
- ―Léon, 1794.[src]
Léon was born to a Moorish mother and a Caucasian father. When he was two, his parents left France, as his mother was forced to return to Spain. Léon was left with a note pinned to his shirt outside the cloister of Saint-Denis, with the monks subsequently bringing him to Madame Margot's orphanage.
Initially, Léon proved difficult, keeping Margot up at night with his crying. He rarely spent time with the other children, playing games by himself with imaginary knights and daring battles in his room. By the age of seven, Léon had discovered every possible escape route from the orphanage.
He frequently challenged himself with impressive feats such as skinning hens while their owners were hanging the laundry, stealing pliers from the doctor before he could pull out his tooth, and swimming across any river he discovered while remaining underwater.
The nature of these feats changed one day, when Léon found an aristocratic boy and girl being chased into the town's catacombs by a gang of Jacobins. Léon followed them and witnessed the siblings running towards a dead end; the girl failed to watch where she was going and plunged into a crevice, to her death. However, by using his knowledge of the catacombs, Léon was able to save her brother. After returning the boy to his teary-eyed mother, Léon felt a calling to ensure justice.
Working with Arno Dorian
Escaping the catacombs
- Napoleon: "You need to learn... a bit of diplomacy. Rose, I trust you'll show the boy to the surface?"
- Rose: "Of course, Commandant [...] Kill him."
- —Rose ordering Léon's death, 1794.[src]
His idealistic goal of saving France led Léon to venture down into the catacombs on 3 August 1794, with the intention of spying on the raiders that had recently arrived in town. Although he succeeded in staying undetected for a day, he was eventually apprehended and brought to the raiders' leader, Captain Philippe Rose. They were then joined by Napoleon Bonaparte, who inquired after Rose's progress before ordering the man to escort Léon to the surface.
However, upon Napoleon's departure, Rose commanded his men to kill Léon instead. While the two raiders argued about who would carry out Rose's order, Arno Dorian arrived and snuck up behind them, though Léon's excitement caused him to give away the Assassin's position. Arno subsequently fought the raiders, following which he freed the boy from his cell.
Arno then revealed his purpose for being there, to retrieve a manuscript from Nicolas de Condorcet, which Léon had in his possession. Promising to hand over the document later, the boy ran ahead and handed the Assassin a Guillotine Gun that he had stolen the day before. The two then worked together to get past the raiders in the next room.
While making their way through the caverns, the pair happened to overhear a conversation between Napoleon and his lieutenant. Léon wanted to stop their plans, but Arno restrained him, believing the effort would be in vain. Following Napoleon's departure, the pair began to argue, leading the boy to storm off into a hole in the wall, where the Assassin could not follow.
Finding the temple
- Arno: "I'll get the artifact, then I'm gone."
- Léon: "Fine. But how? Do you have a map to the temple in your coat?"
- —Arno and Léon agreeing to work together, 1794.[src]
Léon subsequently made it to the surface and returned to the garden behind the orphanage, where he had hidden Condorcet's manuscript. However, Arno arrived shortly after, having tracked the boy, and demanded he be given the document. His idealism rejected by the cynical Assassin, Léon relented and handed over the manuscript.
Shortly thereafter, Arno returned, having decided to help Léon in preventing Napoleon from acquiring the artifact. Concluding that the paten plates on Dom Poirier's list where somehow related to finding the temple Napoleon was looking for, Arno decided to recover them, though he only had clues guiding him to the locations of two. At this, Léon laughed, as the third plate was already in his possession.
The next day, Léon was joined in the orphanage by Arno, who had collected the other two plates. With the help of Margot's candle, they realized the plates formed a map of the catacombs when exposed to strong light. However, Arno then departed on his own, leaving Léon with Margot while he went to find the temple.
The day after, Léon went to the town market, finding Arno behind the orphanage upon his return there. The young boy inquired after the temple's location, which the Assassin had managed to find, but he still needed the key to the door. Léon then informed Arno that he had seen Napoleon's lieutenant in the market; the Assassin promptly departed to find the soldier and procure the key.
Unbeknownst to Arno, Léon followed the Assassin down into the catacombs after the latter had acquired the key. The boy stayed hidden as Arno opened the temple door, witnessing the Assassin being ambushed by Rose and falling into a deep pit. Once the Captain and the raiders had gone, Léon came out and threw a lantern, which Arno had dropped, down the pit. Thanking the boy, Arno ordered Léon to stay out of sight while he recovered the artifact; afterwards, back at the orphanage, the pair embraced before bidding each other goodbye.
- Léon is derived from the Greek word leon, λεων, meaning "lion".
- Léon's name and relationship to Arno is a reference to the film Léon: The Professional.
- Léon is one of the few characters in the game to have a French accent.