Leo is an emerald green colored mutant turtle with sapphire blue eyes.
Leo and his brothers were named after great Renaissance artists from a book Splinter fished out of the storm drain. Knowing the world would be dangerous and there would be a time where they want to explore the outside world, Splinter trained the boys in the art of Ninjitsu.
Splinter knew they would never be accepted in their urban society, so he took them to the sewers, made a home down there, and made the four turtles his children. Yoshi, having to have stepped on that rat, thus mutated into a humanoid brown rat by the name of "Splinter", while Leo and his brothers, after coming in contact with Splinter when he was human, mutated into humanoid turtles. In the end, the Kraang dropped the canister of Mutagen they were holding, causing the turtles and Yoshi to mutate. The Kraang found him and attempted to kill him, but Yoshi fought back hard. Unfortunately, Yoshi gave away his position when he accidentally stepped on a brown rat's tail. When their soon to be father walked passed a strange man, a Kraangdroid, he felt something odd about him and followed. Leonardo and his brothers were once ordinary turtles: when they were infants, they were adopted from a pet store by Hamato Yoshi. He tends to be hard on himself, but his diligence does not go unnoticed he is the favored student of Splinter, whose approval he very much craves. He's the most driven of the four Turtles, training and studying relentlessly.
It's the gap between his aspiration and current situation that is the greatest source of frustration in Leo's life. Unfortunately, he's an inexperienced teen (for the moment at least) with three smart-aleck brothers. The leader of the Turtles, Leonardo aspires to be a brave, decisive, perfect hero.