Like his brothers, Leonardo began life as a turtle hatchling who was accidentally doused in a mutagenic ooze, which gave him a more human-like body and mind.
At the story's beginning, Leonardo led his brothers in the rescue of April O'Neil from a band of thieves who were assaulting her. Leonardo was extremely excited about fighting his first battle, and eagerly told Splinter of their accomplishment, though he attempted to be somber when his father was speaking.
He was intensely dismayed when Raphael brought the unconscious April O'Neil to the lair, but did not protest further when Splinter gave his approval. He stood by while Splinter explained their origin to April, and helped escort her back to her home. After an evening of pizza and jokes, Leonardo insisted on returning home because Splinter would worry. However, they soon discovered that Splinter had been kidnapped and the lair ransacked, devastating the Turtles.
Leonardo's cautious, tactical approach to finding Splinter soon brought him into conflict with Raphael, who wanted to be more proactive in their search. After a heated exchange, Raphael stormed up to the rooftop, where he was savagely beaten by a group of Foot ninja and thrown through the skylight. Leonardo led Michelangelo and Donatello in the battle against the enemy ninja, but they were driven into retreat.
At April's country farmhouse, a guilt-ridden Leonardo kept a constant vigil over the comatose Raphael. When Raphael awoke, Leonardo was overjoyed and apologized for his previous harsh words, and the brothers were reconciled. As Raphael recovered, Leonardo and his brothers spent many days training, but Leonardo was still deeply troubled by the loss of their master.
While he was meditating in the woods, he experienced a psychic connection to Splinter. That night, he led his brothers in meditation, allowing them to briefly contact their father. The following morning, they decided to depart for New York again, in order to free him.
On their first night back, they were attacked by the Foot Clan, a battle that culminated in the Shredder appearing before them. Leonardo fared the best among his brothers, wounding the Shredder's arm with one of his swords, but ended up pinned down at the point of Shredder's spear. Fortunately, Splinter reappeared and defeated Shredder, throwing him from the rooftop into a garbage truck.
Along with his brothers, Leonardo warmly embraced their father, before celebrating their victory.
In the first film, 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; he also joked around with his brothers much more than in other versions of the TMNT. Since the film was mostly based on the Mirage comics, one can best compare Leonardo's personality with his counterpart from the comics. He is rather quiet, always trying to put together a plan before he attacks and is again the one that is closest to Splinter.
In the second film, Leonardo was much more prominent and his leader position was brought into focus. Leonardo is once again sensitive, caring, and humorous in this story, but he now displays far more aggressive leadership tendencies.
Along with Splinter and his brothers, Leonardo was forced to move in with April O'Neil temporarily. During their stay, he led them on a successful battle against a large group of criminals robbing nearby shops.
When Splinter revealed that the ooze had come from the TGRI corporation, Leonardo and his brothers headed there in hopes of finding new answers to their origins. They encountered Tatsu and the Foot ninjas there, and began fighting for possession of the last canister of mutagen.
This loss led to friction between Leonardo and Raphael, as Leonardo believed that their first priority should be finding a safe location for their new home, while Raphael was primarily concerned with find the Foot Clan. A new lair was found mere moments after Raphael left, and Leonardo grew more angry with his brother as they moved their belongings into it.
However, he did not allow this anger to interfere with mounting a rescue for Raphael, which almost led to disaster when the other three Turtles were briefly captured. They managed to escape the mutant wolf and snapping turtle, Rahzar and Tokka, and withdrew to the sewers with Professor Jordan Perry, a scientist whom the Foot had abducted.
Their next confrontation was somewhat more successful: Tokka and Rahzar were knocked down long enough for Donatello to catalyze the anti-mutagen, reverting them back to a normal snapping turtle and wolf. However, this led to Leonardo and his brothers being seen by hundreds of humans in a nightclub as they fought Shredder and their mutant opponents.
Just as the Turtles thought they had defeated Shredder, they discovered that he had instead been exposed to the mutagenic ooze, which transformed him into a "super-Shredder." Along with his brothers, Leonardo escaped into the ocean and was able to swim to shore, leaving the Shredder to be crushed under a falling boardwalk. They returned home, victorious, only to discover that Splinter had learned of their error.
Along with his brothers and Splinter, Leonardo witnessed a magical scepter transport April through time and space to feudal Japan, leaving Kenshin in her place. He was eager to go back through time to rescue his friend, but the situation became substantially more complicated when the Turtles actually did so, as they were exchanged with four horse-mounted honor guards in the middle of a battle. With Michelangelo and the scepter missing, Leonardo led Donatello and Raphael to the nearby castle, which they barely managed to infiltrate without being found out.
They managed to locate and free April, but were confronted by a host of guards who kept them from being able to leave except via a sewer drain. After going out in search of Michelangelo, the three Turtles encountered the rebellious villagers, whose village was under attack by the forces of Walker. After the ensuing battle, Leonardo used CPR to revive a child suffering from smoke inhalation, earning the respect of the village.
Unfortunately, no sooner had the lost scepter been found than Leonardo was forced to hand it over to the mercenary Whit. He led his brothers on another infiltration of the castle, leading to an invasion by the rebel villagers, and defeated Lord Norinaga in single combat before humiliating him openly. When Walker had them at gunpoint, Leonardo taunted the man into trying to kill the "demons" himself, and subsequently frightened him into withdrawing.
With the scepter reclaimed, he briefly toyed with the idea of remaining in the past, but dismissed the idea as selfish. Citing it as their "destiny" to return to their own time, he and his brothers made it back to the present.
Leonardo at this point in the series had become less of a leader, shouting out wise cracks and goofing off with his brothers, a flaw not present in other incarnations of Leonardo. Like his brothers minus Donatello, he seemed at home in ancient Japan. In this film there wasn't much for him to really do, he was just portrayed as a goofball making only a few smart decisions.
In the fourth film, Leonardo has been away for a long time, after being sent on a journey by Master Splinter to hone his skills in becoming a more efficient leader after the Shredder's defeat. April finds him in Central America, and once again, Leonardo's desire for perfection was shown, as even as his real training was over for a year, he didn't want to return because he feared he may still not be good enough. While he was hesitant to return to New York City, he does at the right time to take on the dangerous new force of evil.
His relationship with Raphael is strained as Raphael felt abandoned by Leonardo as well as feeling less appreciated by Splinter. Leonardo's vision of the world is perhaps wider than Raphael's; in the first movie prequel comic, Leonardo becomes angry with Raphael for trying to leave them in order to save a man from being mugged, because there are four heavily armed Triceratons in the sewers who could cause devastation to the city. He becomes further angered when Raphael deserts them mid-battle to help the old man. This conflict suggests that the two brothers operate on different levels of morality, though neither is necessarily wrong. Raphael states in the comic that he was tired of waiting for disaster to fall on his family, and tired of fighting aliens while people in their own neighborhood are being mugged and murdered. Leonardo, on the other hand, believes that the world of men is the responsibility of the police, while Utroms and Triceratons are their domain..., and that they should fight only when there is no one else to solve the problem. This also engages Leo in a contradiction when he stays in Central America, using violence to fight local lawlessness and effectively deserting his brothers because he believes, as Raphael believes, that others need him more. Such parallels suggest that the two brothers are experiencing the same dedication to justice but in different mentality, albeit in very different locales and using different tactics.
In the TMNT CGI movie, Raphael challenges Leonardo after arguing of their own individual sense of justice and the reasons for their actions. Leonardo also discovers that Raphael is the Nightwatcher and they engage in an emotional fight. He is defeated when Raphael breaks his swords and pins him to the floor. Raphael almost kills Leonardo out of anger, then retreats in horror of his own actions because of shame, remorse for his actions, and his brother's deep and confused stare. Leonardo is captured by the Stone Generals and Foot Clan, but is rescued by his family later before the final battle where Leonardo and Raphael finally resolve their differences. Raphael accepts Leonardo as their leader while Leonardo confesses to needing Raphael. In the end he realized that he can do anything if he has his brothers by his side.
- According to the T files on the DVD extras of the 1990 film, Leonardo's:
- Hobbies are collecting candles, if it counts.
- Favorite music is Traditional Japanese, and New Age (for meditating).
- Favorite foods are pizza, rice, fish, sushi, and apples.
- Favorite book is On the Art of War by Sun Tzu.
- Favorite color is blue.
- Is right-handed.
- Height is 5'1.
- Weight is 170 lbs.
- Eyes are brown.