Splinter

Splinter is a major character from the Teenage Mutant Ninja Turtles franchise. He is an anthropomorphic mutant rat and serves as the instructor and father figure of the Turtles, responsible for teaching them about the world and training them in martial arts.

Origins
Splinter's origins have varied significantly across the different TMNT mediums, which are described below.

1987 cartoon
In the first animated TMNT series, Splinter was originally a human man known as Hamato Yoshi, a member of a Japanese ninja clan called the Foot. Highly skilled in his practice, Yoshi had developed a rivalry with fellow clansman Oroku Saki who deeply resented him. During a visit from the Foot's grandmaster at their school, Saki planted a knife on Yoshi in order to frame him for plotting to assassinate the grandmaster. Yoshi fled in disgrace to the United States of America.

Yoshi endured a life of poverty living in the sewers of New York City. Though poor, he lived happily surrounded by a collection of Renaissance art books and the rats that resided in the sewers with him. Not long after he took up residence, Yoshi discovered a quartet of baby turtles that had been accidentally dropped down a storm drain. He kept them as his pets, but they would soon become so much more.

One day, something else came down the drain: a strange glowing ooze of unknown origin that caused any creature that touched it to take on the physical characteristics of whatever creature they had most recently been in contact with. The baby turtles, having most recently been in contact with the human Yoshi, became humanoid and developed sentience. Yoshi, however, had most recently been in contact with the sewer rats and transformed into a bipedal rodent.

With his pet turtles having developed human-like intelligence, Yoshi no longer regarded them as mere pets but as his adoptive children and taught them about the world. He named his four sons after the four great Renaissance masters: Leonardo, Donatello, Raphael and Michelangelo. He also took on a new name for himself: Splinter. Splinter trained his turtles in the art of ninjutsu and provided them with weapons when they reached adolescence, intending for them to fight to protect the people of New York from the shadows.

Mirage Comics & 2003 cartoon
In these continuities, Splinter and Hamato Yoshi are not the same person. Splinter is the pet rat of Yoshi and watched his keeper practice the martial arts, subconsciously memorizing Yoshi's techniques. The pair lived in Japan where Yoshi was a member of the secretive organization known as the Foot Clan and was next in line to assume clan leadership. However, Oroku Saki - The Shredder - initiated a hostile takeover of the clan and attempted to kill Yoshi. Taking Splinter and little else, Yoshi fled to the United States, but the Shredder would follow, determined to finish what he had started. Shredder tracked down Yoshi and murdered him.

Completely alone, Splinter disappeared into the sewers of New York. Some time later, he would encounter the four baby turtles that would become his children and students. They would mutate into humanoid forms after coming into contact with a mysterious glowing ooze, developing intelligence and learning about the world above their home in the sewers. Splinter would name his charges after the great Renaissance artists after reading through several books that Yoshi had left behind and would teach the turtles the arts he had witnessed Yoshi practice years ago.

2012 cartoon
In the CGI-animated Nickolodeon series, Splinter's origins are very similar to his origins in the 1987 cartoon. He lived in a rural part of Japan and was a member of a prestigious martial arts school alongside his adoptive brother Oroku Saki, though Yoshi and Saki's rivalry stems from Saki's jealousy towards Yoshi's relationship with a woman called Tang Shen. Saki and Yoshi competed with one another for Tang Shen's affections, but in the end she chose to marry Yoshi. Enraged, Saki left the school and fled from his home, but he would later come to discover his true heritage lay with the Foot, a ninja clan that had been wiped out years ago by the Hamato clan, Yoshi's clan. Saki would revive the Foot under his leadership and take revenge against Yoshi, murdering his clansmen, his wife Tang Shen, and abducting their infant daughter Niwa to raise as his own.

Following his clan's destruction, Yoshi fled to America and lived beneath the streets of New York where the Foot would hopefully not find him. From there, the events of his and the Turtles' mutations occurred much as they had in the 1987 cartoon series.

Personality
Splinter is many things to the Turtles - A wise sensei, protective parent, loving father, stern disciplinarian, quirky master and Zen philosopher. He is determined to train and protect his family at all costs. The fact that he has gone through decades of ninja training does not only mean that he is always fierce when he fights, but that he's also remarkably in tune with the universe.

Abilities
Both as a human and a mutant, Splinter possesses keen senses and is greatly spiritually attuned. He is a Zen master and a master of the Martial Arts, fluent in all ninja techniques. He seldom uses a weapon, but he is capable of using any martial weapon to great effect. Though in his fifties, Splinter is remarkably strong and fit. His strength and skill are rivalled only by his nemesis, the Shredder.