As a human, Yoshi is a tall and lean Asian man with black hair combed over, black eyes, light flesh-toned skin, and perfect abs.
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.
Splinter, unlike his previous incarnations, is laid-back and very lazy. He is absent-minded and has trouble remembering his sons' names, and even refers 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. 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 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.
This attracted the attention of Baron Draxum, who wished to use Lou Jitsu's DNA to mutate an army that would serve him. It was through this process that the Turtles were mutated from ordinary reptiles, making Lou Jitsu the biological father of their human genes. However, he seemingly freed himself and destroyed Draxum's laboratory, causing Draxum to believe that the Turtles had been killed in the fire. He was then mutated to a rat from currently unknown reasons, took the name of "Splinter," and raised the Turtles as his own sons.
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 Yoroi. 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.
"I will never marry any of them off."
"You will never walk the Earth again, Shredder."
- 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.
- 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 has a slight resemblance to singer Elvis Presley. However, it might be coincidental.
- 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.
- According to Leo, Splinter always falls asleep after eating milk and cake.
- Lou Jitsu's eyewear as a human strongly resembles Simon's sunglasses from Gurren Lagann.