Leon was the oldest of three siblings the youngest of them being mike and the middle one being Scorpia. He inherited the soul shield technique of the family and his took the form of a watery lion he was the favorite of his father who loved his boys more than Scorpia. Leon was raised to take over the family he was taught that grace mattered over strength.
At the age of 10 Leon's little sister Scorpia (age 8) ran away from home where she became Mary's apprentice he never saw her again until the events of the Halloween hustle.

At age 16 leon was asked to summon a servant and when he summoned a servant he got Frankenstein he learned quickly that she hated that name and preferred to be called berserker. Leon was shocked by the way that Frankenstein looked he even commented that victor Frankenstein must have had a twisted sense of beauty to call her a monstrosity. Leon and Frankenstein became fast friends even though she couldn't talk much they always had each other's back and had been together as a team for 9 years before her untimely demise to vlad the implied

Leon at age 22 took over the leo institute after his father died mysteriously he made many changes and expanded the range of the institute. He made an alliance with the order for the rights to search the orders ruins even though he likes Eliza just fine he still is forced to fight her and her children thanks to this alliance. He also made an alliance with the round table after Qwenivere took over so that they could share resources. Not everyone likes him and he can't often be around other people since many would have him killed even from within his own origination most of this was stopped thanks to Berserker.

At age 25 leon is now still head of the organization and one of the front runners in the anti-scorpia movement because he believed he made her the way she is by not being kinder to her.