Leonardo, nicknamed Leo, is a fictional character and one of the four main characters in Teenage Mutant Ninja Turtles comics and all related media. He is often depicted wearing a blue eye mask. His signature weapons are two katanas. Leonardo is the most serious, the most spiritual, the most disciplined, and the most in-line with Splinter's teachings and thoughts, and is the leader of the Turtles.
Original trilogy
In Teenage Mutant Ninja Turtles, Leonardo was fairly modest and sensitive, rarely issuing direct commands and seemingly much more relaxed around his brothers thinking of himself as more of an equal than a leader. It was he who first communicated telepathically with a kidnapped Splinter and seems the most anxious about Raphael's health after his ambush by the Foot Clan. He fought alongside his brothers against The Shredder in the climatic battle and was the only one of the four to actually injure The Shredder, but, like his brothers, could not defeat him. Due to the focus on Raphael in the film's plot, Leonardo's personality was rarely explored and his leader position in the team took a back seat. Leonardo was portrayed by David Forman and voiced by Brian Tochi.  In The Secret of the Ooze, Leonardo was much more prominent and his leader position was brought to focus. He is seen on many occasions bickering with Raphael as their sibling rivalry begins to become much more serious. He, like his brothers, was astonished at the return of the Foot but he found that their current homelessness due to their last battle was a more pressing issue and soon he convinced his brothers that they needed to move. Leonardo is once again sensitive, caring, and humorous in this adaption but he now appears much more bossy and controlling.  In Teenage Mutant Ninja Turtles III, after traveling back in time to feudal Japan, Leonardo leads his brothers to help a village in trouble from the villainous weapons trader, Walker, and to return home.

Q: Who were the original three ninja turtles?
A: unknown
What were the names of the Ninja Turtles?
Teenage Mutant Ninja Turtles,
Teenage Mutant Ninja Turtles,