Master Splinter, once known as Hamato Yoshi and by the stage name Lou Jitsu, is a descendant of the Hamato Clan, a former martial arts movie star and the (partially) biological father and sensei of the Turtles.
As a Human, Yoshi was a tall and lean Asian (presumably Japanese) man with black hair combed over into a pompadour, black eyes, light-toned skin, and perfect abs. His attire usually consisted of outfits resembling wingsuits, with glasses or sunglasses worn over his eyes.
As a Mutant, Splinter is a short, plump rat with grey fur, as well as white fur in his ears, white hair with a section tied into a top bun, white bushy eyebrows and a goatee to compliment. He has golden yellow eyes, a red-pink nose, black whiskers on his cheeks, his arms and legs are pink (with his hands having five fingers instead of the usual four) and a small tear on his right ear. Splinter wears a black hair tie to hold up his white chonmage and a brown yukata with orange trim and red lotus flowers printed on it.
In some episodes of Season 2, his yukata appears to be longer, much like a kimono, and the Hamato Clan symbol is branded on the left side of his chest.
Splinter, unlike his previous incarnations, is laid-back and very lazy. He is absent-minded and even has trouble remembering his sons' names, often referring to them by their mask colors. He also attempts to stir up mischief and trouble with his sons, including stealing the Turtle Tank in "The Fast and the Furriest."
However, he is shown to take action when needed, like in episodes such as "Origami Tsunami" and "Mrs. Cuddles." Also as shown in "The Evil League of Mutants," Splinter deeply cares about his sons and their safety.
Splinter has also been shown to slowly grow more serious as the first season progresses, especially after learning of the existence of the Shredder. He deeply cares about the safety of the Turtles, and as a result he is shown to be strict at times. Although his first on-screen training session was viewing a Lou Jitsu tape (which, given the later revelation, was actually a video of himself), Splinter is very serious in training the Turtles to perfect their fighting skills.
He is a descendant of the Hamato ninja clan who defeated the Shredder 500 years ago and trained themselves to be warriors to fight against the Foot Clan and prevent the Shredder's return. However, Splinter admits he didn't believe in the story and decided to use his martial arts skill to become a movie star.
When shooting for a film, Yoshi met Big Mama, who drove his trailer, and the two started a romantic relationship. However, Yoshi was unaware that she is a Yōkai, despite some obvious signs. After attempting to propose to her, he was thrown into the Battle Nexus, where he triumphed over his opponents. Sometime later, Yoshi had sworn off of fighting in the Nexus and tried to resume a more peaceful lifestyle where he not harm any living creatures.
However, his fame in the Battle Nexus attracted the attention of Baron Draxum, who wished to use his DNA to mutate an army that would serve him. It was through this process that the Turtles were mutated from ordinary reptiles, making Yoshi the biological father of their human genes. However, unwilling to watch innocent creatures be turned into monsters for Draxum's cause, Yoshi freed himself and destroyed Draxum's laboratory, causing Draxum to believe that the Turtles had been killed in the fire. In the midst of his escape, Yoshi released Draxum's other test subjects and a rat bit his finger just after his exposure to the ooze, causing his mutation. He doesn't remember everything from his transformation into his current form.
Splinter remained unaware of his sons' contact with Draxum and the Foot Clan until the events of "Shadow of Evil". Upon discovering evidence of the Foot Clan, he impersonated a teenager and managed to spy upon his enemies, discovering that they were reassembling the Kuroi Yōroi. Realizing that this foreboded the possible return of the Shredder, Splinter pretended to be a member of the Clan in order to take a piece of the armor. This attempt was thwarted by Draxum and, unwittingly, his sons. Upon escaping without the armor piece, Splinter promised to tell his sons "everything" and stated that they were "way behind" on their destiny.
As reflected in his status as the most popular martial arts movie star of all time, Splinter is a very skilled fighter, capable of defeating all four of his sons at the same time even when out of shape. He has also shown to be an extremely adept improvisational fighter, using items such as fish and ladders as weapons.
- Leonardo: Leo was the one that would get on his bad side most of the time. But there are times that he gets impressed by him, he even makes him leader in the season 2 finale.
- April O'Neil:
- Piebald: Piebald was his beloved pet fish.
- Todd Capybara:
- Baron Draxum: Baron Draxum used Lou Jitsu's DNA to mutate the Turtles into part-humans.
- Mrs. Cuddles: Splinter hates Mrs. Cuddles for kidnapping his family and her show taking over his TV schedule.
- Big Mama: Before Splinter became a mutant rat and met Baron Draxum, he was Big Mama's boyfriend in his years as Lou Jitsu and wanted to marry her, but after Big Mama showed her yokai form to Lou Jitsu, she captured him and made him a competitor in the Battle Nexus. Years later as a single father of four, Splinter still has some affection for Big Mama, but is now fully aware of the monster she is. Big Mama shares said feelings but only in a manipulative and duplicitous manner.
- Shredder: The Hamato Clan was in possession of the Kuroi Yōroi's face plate for generations as a family heirloom, which they had come to use as a tea kettle. The reveal of the Shredder being real is what led Splinter to take training the Turtles more seriously.
- Foot Clan: The Foot Clan are the sworn enemies of the Hamato Clan. Splinter's exact relationship beyond this is unknown.
- Kristoff Van Bradford: Splinter describes him as "An Atrocious Actor Who Is Dishonorable To His Core". He hated him for taking over his Lou Jitsu Dojos and his dishonored cheating ways of fighting.
"I will never marry any of them off."
"You will never walk the Earth again, Shredder."
"Oh, and Blue you are the leader now"
- Splinter is voiced by Eric Bauza, the same actor who voiced Tiger Claw in the 2012 TV series.
- Throughout most of Season 1, it was hinted that Splinter was once Lou Jitsu (and Hamato Yoshi).
- Throughout Lou Jitsu's appearances until "Shadow of Evil", he has been credited as "Additional Voices" and not as "Lou Jitsu".
- Like with most celebrities, he keeps copies of most of his merchandise. But the episode "Late Fee" suggests he may not keep copies of all his own films, as he had rented one of his films and the episode's plot involved his sons' attempts to return it on time.
- The name "Lou Jitsu" appears to be a pun of the term jiu jitsu, an outdated romanization of the word jūjutsu (柔術), which is the name of a Japanese martial art. The former variation is still used in derivative arts, such as brazilian jiu-jitsu.
- Lou Jitsu's human form slightly resembles the singer Elvis Presley. and the actor Jackie Chan. According to an interview, the reason that Splinter looks like he's gained a few pounds is because since there's no Shredder in the new series, Splinter has no exact reason for training the Turtles.
- However, after they learn about threats such as Baron Draxum and the fact that the Foot Clan is planning to revive the Shredder, he begins training the Turtles more seriously.
- It is also possible that Splinter was lazy because he did not want to focus on combat following his time in the Battle Nexus.
- According to Leo, Splinter always falls asleep after eating milk and cake.
- Lou Jitsu's eyewear as a human strongly resembles Kamina and Simon's sunglasses from Tengen Toppa Gurren Lagann.
- While in Big Mama's Battle Nexus, Lou Jitsu briefly had a pet rat. This was a reference to previous incarnations of Hamato Yoshi having a pet rat that would later became Splinter.
- Splinter is the first mutant to not get arrested in the Tales of the Hidden City. Second being Michelangelo.