As a human, Lou Jitsu is a tall and lean Asian man with black hair combed over, black eyes and light flesh-toned skin.
As a mutant, Splinter is a short, plump mutant 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 as he often sits in the chair. He is absent-minded and has troubling remembering his sons' names, and even refers to them by their mask colors. He also prompts 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. Aside of deeply caring and concerned of the safety of the Turtles, he is also shown to be strict. Although his first on-screen training session was of viewing a Lou-Jitsu tape, Splinter is very serious in training the Turtles to perfect their fighting skills.
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, and he raised the Turtles as his own sons.
- 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, they keep copies of all their merchandise.
- The name "Lou Jitsu" appears to be a pun of the term jiu jitsu, an old-fashioned variation of the word jūjutsu (柔術), which is the name of a Japanese martial art.
- 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 falls asleep after eating milk and cake.