Leo is the child of a world known spelunker and a top female executive of the biotech firm, G Corporation. Leo’s father disappeared during an exploration when Leo was a child, but even so, Leo strove to become just like him. Leo grew up to be a straight and narrow person, but Leo's happy days came to an abrupt end when Emma Kliesen was killed. Saddened by the tragic event, Leo shut everyone out. Some time later, the police inconclusively ended the murder investigation without explanation. Leo continued the investigation.
Leo's gender was revealed during the showing of Tekken: Blood Vengeance in Germany. Leo is a girl, and her full name is Eleonora "Leo" Kliesen