Léon was left at an Orphange, that housed children to be 'played' with when they reached a certain age. As soon as he turned 7, he was left in the middle of nowhere, in a forest. Killing vicious animals, eating wild food, etc. He somehow survived. Now he was 20, learned all the tactics of survival. Due to him being left alone to survive by himself when he was a kid, Léon became a skillful Assassin. But there was also another result which was that he had no more emotions, like some robot. Now he lives for himself, only for himself.