Leonardo, commonly nicknamed Leo, is a superhero appearing in Teenage Mutant Ninja Turtles comics and related media, and created by American comic book artists Kevin Eastman and Peter Laird. He is one of the main characters of the franchise, along with his brothers, Donatello, Raphael and Michelangelo. Leonardo is traditionally depicted as the leader and strategist of the turtles. Often shown wearing an ocean blue bandana, his signature weapons are a pair of swords (named katanas in many versions of the series). He is traditionally portrayed as the most mature and disciplined of the Turtles, displaying a stoic demeanor and a strong sense of responsibility. Like his brothers, he is named after an Italian Renaissance artist, in this case Leonardo da Vinci. In the original comics, all four of the Turtles wear red masks, but for the creators to tell them apart, he was written and redrawn to have an ocean-blue mask.

The Teenage Mutant Ninja Turtles (often shortened to TMNT or Ninja Turtles) are a fictional team of (usually) four teenage anthropomorphic turtles - Leonardo, Donatello, Raphael, and Michelangelo - named after four Renaissance artists, who were trained by their anthropomorphic rat sensei, Splinter in the art of ninjutsu. From their home in the storm sewers of New York City, they battle petty criminals, evil overlords, mutated animals, and alien invaders while attempting to remain isolated from society. Other characters in the franchise include April, Bishop, Bebop, Rocksteady, Shredder, Krang & Jennika.