Splinter is a protective parent, stern disciplinarian, quirky master and Zen philosopher. Having lost a family once, he is determined to train and protect his new one at all costs, though he grudgingly realizes that they’re at an age where he will have to, at some point, give them the freedom to make their own mistakes. He is a ninja master at the height of his abilities----so in tune with the universe that he can literally feel it's vibrations, allowing him to project and sense energy, and the intentions of others.
Originally a human named Hamato Yoshi, Splinter lived in Japan and studied ninjutsu alongside his friend, Oroku Saki (later known as The Shredder). However, both men fell in love with the same woman, Tang Shen, which sparked a bitter rivalry between them. Eventually, Tang Shen married Yoshi and gave birth to their daughter, Miwa. One night, Saki, mad with jealousy and hatred, attacked Yoshi in his home, intending to kill him. During the battle, the house caught fire and Saki left Yoshi to die. While Yoshi survived the fire, Tang Shen did not, and their daughter, Miwa, had supposedly died.
Devastated, he gave up his old name and left Japan. As Splinter, he came to live in New York City. One fateful day, he bought four baby turtles at a pet store. As he was walking down the street, he bumped into a suspicious man, whom he followed into an alley. As Splinter watched the first man exchanging a canister of ooze with another, he stepped on a rat that gave away his position. A fight ensued, and while Splinter defeated the men, the canister was broken. Splinter and his pet turtles were all covered in ooze and mutated instantly. He became a giant rat, and the turtles became humanoids.
For the next fifteen years, Splinter and the turtles lived in hiding in the sewers under New York City. Taking them as his sons and students, Splinter raised the turtles and trained them in the ways of Ninjistu. When they turned fifteen, Splinter reluctantly allowed them to leave the lair for the first time.
In Rise of the Turtles, Part 1, Splinter is seen telling the story of his mutation to the turtles. He had also kept the canister of mutagen as a souvenir. As a celebration of the turtles' fifteenth birthday, Splinter allows them to explore the wonderous streets of New York.
In Turtle Temper, Splinter explains to a grumpy Raphael that anger can jeopradize the people around you. Once again, Splinter reveals his past. He explains that his temper against the Shredder caused his own family to be killed.
In New Friend, Old Enemy, Splinter only briefly appears when he recognizes a farmiliar move used by Leonardo in a sparring match. They realize that Mikey's recently made friend, Chris Bradford, is one of Shredder's top students.
In I Think His Name is Baxter Stockman, Splinter unexpectedly catches the turtles misbehaving and skateboarding in the lair. He grounds them for a week, but they sneak out against Splinter's will and encounter a lone man dressed in robotic armor named Stockman. At first, they defeat him easily, but the fight turns into more than they expect.
In Monkey Brains, Splinter becomes fascinated in April when he realizes that she has an ability to sense internal feelings. As a response, Splinter wants to teach her to be a kunoichi.
In New Girl in Town, Splinter explains to Leonardo that leadership is about responsibility. Raph believes that being a leader is easy, but is proven wrong when he is put through the same stress that Leo is.
In Baxter's Gambit, Splinter assists April in finding a suitable weapon for her. At first, she cannot use the weapons, until Splinter offers her a katana-like tessen that he once intended to give to his daughter. This likely indicates that Splinter views April as his daughter-figure.
In Karai's Vendetta, Splinter teaches the turtles and April that they can use anything to defend themselves if the situation calls. He uses Raph as an example, whom he licks in order to get him off. The Shredder sends Karai to capture April in order to lure out the turtles, but April is able to apply her Ninjutsu knowledge to flee the situation. Back in the lair, the turtles congratulate April. Splinter, who is skeptical, tells April that she still may be unsafe, due to the simultaneous threats that the Shredder and the Kraang pose, advising that April should not leave the lair. April, reluctant to cope with the circumstance, is eager to get started on stopping the enemies.
In Pulverizer Returns!, Splinter realizes that the turtles have grown complacent using their signiature weapons, and that they will have to adapt to using varied weapons.
In Booyaka-Showdown, Part 1 and Part 2, While the turtles are forced to confront the Kraang and rescue April, Shredder uses April's abduction to trick Splinter into confronting him. Although initially amused at the discovery of Hamato Yoshi being a mutant rat, Shredder quickly engages him in battle, angrily proclaiming that Hamato stole everything from him, while Splinter counters that Tang Shen was never Shredder's. Initially evenly matched, Splinter gains an advantage when he starts to rely on his abilities as a rat, breaking one of Shredder's blades in his teeth and running on all fours to evade his attacks, but is knocked off-balance emotionally when he realizes that Karai is his own daughter, Miwa, raised to hate him and believe that he was responsible for her mother's death. Unwilling to fight his daughter, Splinter retreats, declining to tell his sons what he has discovered, in favor of allowing them celebrating their supposed victory over the Kraang.
Splinter seems to be very adept in the mind. For instance, when Rat King attempted to hypnotize him, Splinter was able to defend himself from Rat King in his dreams. Splinter has perhaps trained in the ways of ninja for all of his life, which makes him very methodical in physical situations, and able to act easily in difficult situations that require thought. Even though his mental fight with Rat King was strenuous, he still easily defeated Rat King with his sons' help, showing that he had to combine his thoughts with his physical power, which ultimately led him to nearly kill The Rat King. Splinter's feelings for his former family; his daughter, Miwa, who was stolen by his arch-nemesis, and his deceased wife, who was killed in battle, and his determination to hold onto his current bond with the turtles...gives him the abilities he has today. He can also seemingly read his opponents thoughts and predict their next move, implying that he can sense the projections of opponents. This seemed to be evident during his fight with Shredder, during which Splinter also demonstrated his ingenuity by using his natural abilities as a rat in the fight (something that he had never shown before, as he focused on training the turtles in more human skills), such as catching Shredder's blade in his teeth and running on all fours. Despite The Shredder taunting him about his daughter, Splinter nearly defeated him, until Karai made her interference.
Leonardo - The oldest of Splinter's four adpoted sons and the leader of his 3 younger brothers. Splinter seems to share most of his knowledge with him. However, it is just in hopes of embracing Leo's role as the leader, and making him more tactful and intelligent.
Raphael - The second oldest of Splinter's four adopted sons and the most aggressive of his brothers. Him and Splinter are shown to have similarities in their temperament, such as when Splinter retaliated on The Shredder, which resulted in the tragic death of his own wife. And later, when an arrogant man caught the turtles on video with an I-Phone, Raph sought to break it. However, the knowledge that Splinter had acquired from the result of his temper against Shredder told Raph that he must maintain his temper...in order to get the best of the situation.
Donatello - The second youngest of Splinter's four adopted sons and the most technological of his brothers.
Michelangelo - The youngest of Splinter's four adopted sons and the wildest of his brothers. Splinter says that Michelangelo can fight easily without thinking. Despite Mikey's dimwittedness, Splinter claims that he shows great potential (most likely in agility).
Karai - Splinter's initially supposed dead daughter, Miwa, who was taken by Oroku Saki after the events of their final battle and raised as his own daughter. Splinter only found this out upon being forced to duel with the Shredder, after April O'Neil's abduction. Once he knew the truth, he refused to fight her, leaving her and his enemy alive. Even though Miwa is out of Splinter's life in one sense, Splinter still has one place that he holds her—his heart.
Tang Shen - Hamato Yoshi's wife, who died a long time ago. It seems that Shredder loved her too. Splinter loved her dearly and blames himself for her death.
April - A teenage girl who met Splinter and the turtles after being kidnapped by the Kraang. Since he lost his true daughter many years ago, he has come to view April as his surrogate daughter, and he even supplied her with the weapon that he intended to give to Miwa.
Leatherhead - More of an ally of the turtles.
Shredder - Splinter's old friend and current arch-nemesis. They fought over Tang Shen when Saki was consumed with jealousy, which resulted in Splinter's house catching ablaze and collapsing on Shen, killing her. Up until this day, Splinter has never forgotten about that moment. Unbeknownst to Splinter, Shredder stole his daughter, Miwa, during the night of the tribulation and raised her as his own daughter. He began teaching her in the ways of the ninja, and later convinced her that Splinter was responsible for her mother's death (which is, of course, not true). Recently, Shredder has organized an army of ninja called the Foot Clan, whom he deploys to locate Splinter and his disciples after learning of the latters' whereabouts (New York City). Eventually, Splinter and Saki duel once more, during which Splinter discovers the truth—that Karai is his own daughter, raised to hate him and the turtles. This both infuriates and depresses Splinter...when discovering that his daughter has been dealt with in the wrong hands.
Chris Bradord ("Rahzar") - Splinter has only battled with him once upon confronting the Shredder. Splinter is relatively more skilled in combat than Bradford.
Xever ("Fishface") - Splinter has only battled with him once upon confronting the Shredder. Splinter is relatively more skilled in combat than Xever.
'Dr. Victor Falco - Has attempted to (and succeeded at) taking over Splinter's mind, while under the alias of the "Rat King' by using deceptive tactics based upon their similarities.
"Raphael, there is no monster more dangerous than a lack of compassion." (sees Leatherhead) "My mistake..." -It Came From the Depths
"Of course. I am compassionate, not insane." -It Came From The Depths
"That's the choice I made. What choice will you make?" -Turtle Temper
"I hope you have learned, turtles, that truth is not the only thing that hurts!" -I Think His Name is Baxter Stockman
"The first rule of being a ninja is do no harm. Unless you need to do harm, then do lots of harm!" -I Think His Name is Baxter Stockman
"You were all very lucky. (Raphael responds) Few have ever faced the Shredder and survived. (dialogue) Perhaps. But that no longer matters. It is clear now that the Shredder is a problem that will not go away. So prepare yourselves, my sons... because as of this moment... we are at war...!" -The Gauntlet
"Yes, because you will stay down here until you are ready! No patrol, no games, no rest! There is only training! Starting now!" -Panic in the Sewers
"If I were the Shredder, none of you would be breathing right now. Understand!?" -Panic in the Sewers
"No, I am a man...! I am Hamato Yoshi!" -I, Monster
"My place... is with my sons!" -I, Monster
"Oh, the Olympics?" -TCRI
"You fool...! Do you have ANY idea what you've done!?" -Booyaka-Showdown, Part 1
"Look closely at this face, Shredder. For it is the last thing you will ever see!" -Booyaka-Showdown, Part 1
"You took everything that I loved. Everything! And still you hunt me down! So... I fight you now... to end this!" -Booyaka-Showdown, Part 2
"You never had anything but your hatred! And if you defeat me, you will have NOTHING!" -Booyaka-Showdown, Part 2
"... Miwa?" -Booyaka-Showdown, Part 2
"I lost many things... My family, my home... my name... But I gained many things as well, like the four of you." -Rise Of The Turtles, Part 2
- Splinter's given, "Yoshi", (喜), translates as "like, love, enjoy", or "joyful thing". Splinter's surname "Hamato" (濱戸), translates as "beach/sea coast/river bank door/family". If written purely in hiragana, "Hamato Yoshi", (はまとよし), means "Alright still".
- So far Splinter has appeared in every episode of the series except for two: "Cockroach Terminator" and "Parasitica".
- He has faced Shredder in the Season 1 finale, winning the battle physically but losing it emotionally.
- In the season one finale, Splinter found out that his daughter, Hamato Miwa, is still alive.
- This is the second version of Hamato Yoshi being mutated into a rat, the first version being from the 1987 seires.