Leon initially introduced himself as a member of the Dark Cooking Society. He first appeared at the Yang Spring Restaurant demanding that Ruoh give him one of the Legendary Cooking Utensils that he says he is entitled to. Ruoh then said that he had to battle Mao in order to find out the utensil's true successor. The battle was won by Mao and Leon soon revealed everything to him after realizing that he still loves cooking, and like Mao, Leon is also the successor to the Ever-Soul knife. Leon revealed that he betrayed and escaped the Dark Cooking Society after realizing the kind of organization they are.
It turns out that a young Leon was a cook for the Yang Spring Restaurant a few years ago. Like Mao, Leon was a natural genius in the field of cooking. He was also a kind child; not wanting to kill animals, but when he does, he places a red paper talisman on the dead animal and prays for it. Since he wanted to learn more about cooking, he left the restaurant and ventured around China. During his travels, he began to grow a strong urge to become a better cook, but when he couldn't find anymore suitable things to learn, he decided to join the Dark Cooking Society in order to learn their Dark Cooking Techniques. While in the Underground, his knife skills evolved to an unreachable level. Corrupted by the organization, he became even more obsessed in becoming the best chef. He sought out Luo Xie, the best knife forger in China, and had him forge the best knives. Luo Xie called his creation the Seven-Star Knives, the best knife set in all of China. On a cliff top, when Luo Xie said that he will one day create a better set, Leon was enraged, and in a fit of anger, stabbed him in the abdomen, causing him to fall off. This traumatized Leon and began to make things right from that point. He is the only person who possesses the coveted Seven-Star knives. Although, on the episode "The True Owner of the Seven-Star Knives", he encounters an Underground female chef, Shan An, who possesses duplicates.

He travels with Mao retrieving the Legendary Cooking Utensils, in order to prevent the Dark Cooking Society from possessing them.

(Source: Wikipedia)