Leonardo Bistario Harwey is the Master of Saber in the Moon Cell's Holy Grail War in Fate/Extra and the heir of the Harwey family.

He is the younger half brother of Julius B. Harwey who is unqualified to lead the Harwey family. When he was 3 years old, the Harwey family invested in him as he shows great potential. He undergone repeated surgery as a child, including a sound thaumaturgical process to burn knowledge directly into his brain.

Believing the Holy Grail to be potentially dangerous to humanity, Leo participates in the Holy Grail War to secure it. He doesn't concern himself with subtlety or tactics, instead letting something destined to be revealed happen without question. Victory is all but assured to him, as his superiority over others has been reinforced every day since he was born. Though he was raised to be a perfect ruler, he lacks normal human emotions.
(Source: TYPE-MOON Wiki)