Leonardo (or Leo), a fictional character, is the eldest of the four Teenage Mutant Ninja Turtles (TMNT). He is distinguished by a blue bandanna (although originally all four Turtles had red bandannas) and his weapons are two ninjaken (literally "ninja sword"), which are universally referred to as katana. Leonardo takes after his sensei, Splinter, in taking ninjutsu very seriously.
He spends much of his free time in practice and meditation. He has a strong sense of honor, and is a strict follower of the Bushidō code. He often speaks for his brothers and tries to keep them in line, making him the de facto leader of the team, and often the lead protagonist of various TMNT stories.
In the fourth feature film, "TMNT", Leonardo is stated to be the eldest of his brothers, although the relative ages of the Teenage Mutant Ninja Turtles are not officially stated. He is named after Leonardo da Vinci. In Volume 1 of the original comic series by Kevin Eastman and Peter Laird, Leonardo plays an important role.
At the beginning of the series, he is fifteen. In the early stories, he is not explicitly referred to as leader, though he usually speaks for the team. Further in the series, he openly states his position as leader to Raphael in "Teenage Mutant Ninja Turtles #44," 1992.
He is the team's primary strategist (except in situations related to technology, Donatello's field). In Leonardo #1, Leonardo goes out for a run on the rooftops of New York City and is ambushed by the Foot Clan. He puts up an admirable fight against the Foot soldiers, but is eventually overwhelmed by them and rendered seriously injured and nearly unconscious.