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Leonardo (or Leo) is a fictional character that appears in the Teenage Mutant Ninja Turtles comics and all related media.
In the Mirage comics all four turtles wear red bandanas, but in other versions, he wears a blue bandanna. His signature weapons are two ninjaken (literally "ninja sword"), which are universally referred to as katana. Throughout the various media he is depicted as the leader of the four turtles and the most disciplined. He is named after Leonardo da Vinci.
Leonardo is depicted as the eldest brother and (along with Donatello) the calmest of the four. He never explicitly referred to himself as leader in the early stories, except issue #42 ("The Violent Underground"). He is the one to usually take charge of the turtles when Master Splinter is not present. He is often at odds with his more hot-headed brother, Raphael.
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 an army of Foot Ninja, but is eventually overwhelmed by them. Beaten to near unconsciousness, he is thrown through April O'Neil's apartment window. The remaining Turtles and Splinter are forced to continue...