Leo, full name Eleonore Kliesen is a bājíquán practitioner from a very talented family. Her father was a world-famous spelunker, while her mother, Emma Kliesen served as a G Corporation executive.
Although Leo's father disappeared during an expedition when she was a child, she still wanted to follow in the family tradition and become a spelunker. Leo possessed a strong sense of character, thanks to a proper upbringing. Life was pleasant and relatively uneventful until one fateful day when her mother was killed by an unknown assailant. Depressed and filled with grief, she became incensed when the police called-off their investigation quickly and without explanation. She vowed to find the truth.
Source: Wikipedia, "List of Tekken characters", available under the CC-BY-SA License.