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 its 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 (also 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 his daughter Miwa. One night, Saki, mad with jealousy and hate, 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 his daughter Miwa was lost.
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 man, he stepped on a rat that gave away his position. A fight ensued, but 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 under New York City in their sewer lair. Taking them as his sons and students, Splinter raised the Turtles and trained them in the ways of ninjutsu. When they turned fifteen, Splinter reluctantly allowed his sons to leave the lair for the first time.
- 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 one: "Cockroach Terminator".