Hamato Yoshi

Hamato Yoshi (濱戸喜, "Hamato Yoshi") is a central character from the Teenage Mutant Ninja Turtles comics and all related media. In all continuities, he was once a great and honorable ninja whose story is always closely intertwined with that of Splinter: he was the owner of a pet rat who becomes Splinter in the original comics, original films, , and the 2003 animated series, while Splinter was Hamato Yoshi in the 1987 animated series, the "Adventures" comics, the IDW comic series, the 2012 animated series, and the 2018 animated series.
Comics.
Hamato Yoshi was the greatest shadow warrior of the Foot Clan in Japan. He owned a rat named Splinter, who copied his movements as he practiced ninjutsu. He was romantically involved with a woman named Tang Shen. However, their relationship attracted the jealousy of Oroku Nagi, who also loved Shen. When Nagi was rejected by her, he became enraged and violently beat her. Shortly after, Yoshi arrived and, coming to Shen's defense, slayed Nagi. He was dishonored for having killed another member of the Clan and forced to choose between suicide or exile to another country. He chose the latter, and left with Shen and Splinter to the United States. Years later, Nagi's brother Oroku Saki climbed the ranks of the Foot to become the leader of its New York branch. He followed the two lovers to New York City and killed them both in vengeance of Nagi. However, the rat Splinter escaped to the sewer for safety. Some time later, Splinter witnessed a truck carrying toxic waste swerve to avoid colliding with a blind man as he crossed the road. A canister containing neon green glowing liquid fell into the sewers, while a boy coming out of a pet store dropped his four baby turtles into the sewers. Splinter and the four turtles came into contact with the radioactive substance and mutated into intelligent, humanoid beings.
1987 animated series & "TMNT Adventures".
In the 1987 "TMNT" cartoon and the "TMNT Adventures" comics that followed, Hamato Yoshi and Splinter are the same character, and the romantic subplot was eliminated. In the Japanese dub of the 1987 series, his name is "Takeshi Yoshihama" ( "Yoshihama Takeshi").
Hamato Yoshi was once the Shidoshi of the Foot Clan in Japan. One of his students Oroku Saki framed him for attempted murder of a visiting master sensei, and had him exiled to New York, where Yoshi was forced to live in the sewers in shame, and befriended the rats. Years later, when Saki moved to New York himself, he dumped mutagen into the sewers to kill Yoshi. Instead, the mutagen caused Yoshi and his four pet turtles to mutate. Yoshi himself mutated into a humanoid rat, as the last animal he was in contact with before he stepped into the mutagen were rats, even though he picked up the turtles just after he touched the mutagen (he tried to clean the mutagen off of them right before they mutated into their humanoid forms). Yoshi took on the nickname "Splinter" as given to him by the turtles themselves because he could break wooden boards into splinters. He then proceeded to teach ninjutsu to the Turtles, to teach them self-defense because those who are different are feared by many.
In the Season 2 episode "Splinter No More", Donatello finds a remedy to the mutagen effect and uses it to turn Splinter back into Hamato Yoshi. He thus returns to the surface and the streets, but finds it difficult to re-adapt into normal everyday human life. As the effects of the remedy soon wear off, Hamato Yoshi turns back into Splinter and returns to the Turtles with few regrets about leaving his human life behind.
Films.
Yoshi's story, as explained in the first of the four TMNT movies, mirrors that of the comics, although Oroku Nagi is completely removed from the story, and Yoshi's conflict is with Oroku Saki himself. Hamato Yoshi is seemingly portrayed as a construction worker and Yoshi and Saki are portrayed as rival members of the same clan who constantly competed against each other, with their competition for Tang Shen's affections being particularly fierce. Instead of fleeing from the murder of a clan member, Tang Shen persuades Yoshi to flee to America to avoid fighting Saki (presumably to the death) for her hand in marriage. Saki vowed vengeance and spent years searching for them. Saki eventually finds and kills Yoshi and his wife in their New York apartment, leaving Yoshi's pet rat Splinter homeless. The actor who played him was uncredited.
In the third "Teenage Mutant Ninja Turtles" film, the turtles save a child named Yoshi from a burning building in 17th century Japan, Michelangelo getting him out of the building and Leonardo subsequently performing CPR. This Yoshi's relationship with Hamato Yoshi is never fully explained, but based on the past incarnation of another character that the turtles meet on this adventure (a possible British ancestor of Casey Jones, Whit) a direct relationship between this boy and Hamato Yoshi seems implied. If this is indeed the case, then by saving the boy's life, the turtles had also saved their own future, as their origin is inexorably tied to the fate of Hamato Yoshi.
In the 2014 reboot, Hamato Yoshi does not appear anywhere in the turtle's new origin story. However Splinter remarks to April that he does not remember a time before living in Sack's laboratory. This implies there may be a wider story in the origin of the turtles and Splinter.
2003 animated series.
In the 2003 cartoon, Hamato Yoshi's background was once again thoroughly revised. He was no longer a former member of the Foot Clan. His new origins are described in the season 4 episode "A Tale of Master Yoshi".
Hamato Yoshi was an orphan, who, along with his best friend Yukio Mashimi, begged in the streets of 1960s Japan. When Yoshi returned a 5-yen coin dropped by the Ancient One, he took the two of them in for his honesty, and raised them both as his sons, training them in the art of Ninjutsu. The two boys grew up together in the same house, and learning the same arts. Unfortunately, they both also loved the same girl, Tang Shen, another orphan the Ancient One had taken in. Tang Shen loved Yoshi more. During this time, Tang Shen spared a rat (Splinter) that had sneaked into the house, and took it as a pet. One night, Yoshi, Shen, and Mashimi observed a lone man being attacked by four ninja. The two young men decided to help him, and fought off the ninja, who were members of the Foot Clan. The man they saved was none other than the Utrom Mortu. Impressed by their skill, and having been partially exposed when his robotic arm was sliced off in the battle, Mortu gave Yoshi and Mashimi the offer to become Guardians, which they both accepted over the objections of their master.
As a Guardian, Yoshi was promoted time and again, but Mashimi never seemed to advance. Mashimi grew jealous as Yoshi surpassed him in every way, and in his anger, he murdered Tang Shen and betrayed the Utroms to Ch'rell. Yoshi and the Utroms escaped. When Yoshi discovered what had happened he went into a rage, stormed the Foot's citadel and slew Mashimi in single combat. With their Tokyo headquarters compromised, the Utroms relocated to New York, under the name of TCRI. Yoshi went with them, taking along Tang Shen's pet rat, which he named Splinter, to remind himself of what he had done and what he had failed to do.
The Shredder eventually tracked Yoshi down, and tried to force him to reveal the location of the Utroms. Yoshi resisted, and was killed for his defiance. Splinter witnessed the brutal scene, escaped and fled to the sewers, where he mutated along with the Turtles. He then proceeded to teach ninjutsu to the Turtles as he himself had learned it from Yoshi. In the "lost season" (Season 5), of the series, it is learned that Yoshi and the Ancient One had tried, in vain, to get the Ninja Tribunal's help in the fight against the Utrom Shredder. They refused as he was not the "true" Shredder even though the Utrom Shredder was growing in power. Due to their refusal to help, Splinter partly blamed the Ninja Tribunal for Yoshi's death.
Yoshi, a former Battle Nexus champion, is seen in flashbacks of the history of the Battle Nexus. A statue of him is in the hall of champions of the Nexus, and next to him are statues of Splinter and Michelangelo, who won the following two tournaments. Before the Utroms departed Earth, they gave Splinter an orb that contained a hologram of Yoshi. That orb was destroyed by the Utrom Shredder's adoptive daughter, Karai, when she attacked the Turtles' lair in the episode "Scion of the Shredder".
In the fifth season's final episode "Enter the Dragons Part II", a spirit of Hamato Yoshi appears, summoned by the combined power of the Turtles' dragon avatars, and defeats the Tengu Shredder, the aforementioned "true" Shredder. After delivering the final blow against the Tengu Shredder, he exchanges a brief greeting with Splinter before he disappears. 
2012 CGI series.
Splinter is/was known as a wise sensei, a protective parent, a loving father, a stern disciplinarian, a quirky master, and a Zen philosopher. He was born Hamato Yoshi in Japan and was part of the Hamato clan until the destruction of his family - including his wife, Tang Shen and presumably his daughter, Hamato Miwa (later found), and his clan at the hands of Oroku Saki, later to be known as the Shredder. After arriving in New York in exile, he buys 4 turtles and while on his way, he is exposed to mutagen which changes him into a rat. In "'Tale Of The Yokai'", Oroku Saki (the Shredder) accidentally injures and kills Tang Shen while trying to kill Hamato and then takes away Miwa, much to Hamato Yoshi's despair and devastation as he believes that he lost all his family. The turtles save Hamato Yoshi from his death-which was in fact why they had "accidentally" ended up in the past-and go back to the present. 
In the Season 1 two-part finale "Showdown" it is revealed that Karai is Hamato Yoshi's biological daughter, Miwa, whom Shredder abducted after accidentally killing Tang Shen, to get back at him. In "The Wrath Of Tiger Claw", Yoshi shows Karai the same photo she carries of her mother Tang Shen, proving Oroku Saki has lied about being her father. In 'Vengeance Is Mine, Hamato Yoshi's daughter was mutated into a mutant snake, much to Hamato Yoshi's despair. In "The Invasion", Hamato Yoshi battles the Shredder, but loses and is left to drown until Karai saves him. In "Vision Quest" Hamato Yoshi's spirit (which was detached from the body) guides the turtles to face the spirits of the forest. In "Return To New York", April O'Neil, Casey Jones and the Turtles return to see that Hamato Yoshi lost his sanity (which April then heals). In "The Deadly Venom", Karai is brainwashed by Shredder's brain-worm as Hamato Yoshi teaches Leonardo "The Healing Hands." In "The Fourfold Trap" Hamato Yoshi uses "The Healing Hands" to get rid of the worm that was possessing Karai. Unfortunately, much to Hamato Yoshi's despair, Karai fell and was flushed away into the sewers. Hamato Yoshi's healing hands worked because Karai was able to free herself from the brain washing worm.
In the episode "Annihilation Earth", the Triceratons, another species of aliens that are antagonistic to the Krang, threaten to destroy Earth. Hamato Yoshi decides to seek help from Shredder while April informs him that if the Triceratons win, they will never find Karai again. Despite everyone trying to save Earth, everything fails. As Hamato Yoshi attempts to terminate the countdown of the Black Hole, Shredder kills him and the Turtles, April, and Casey are seen mourning. As Hamato Yoshi falls and closes his eyes, the black hole activates and sucks absolutely everyone in except for the turtles, April and Casey, who are rescued by a mysterious new ally known as the Fugitoid. The Fugitoid takes them back in time six months in an effort to prevent Earth's destruction, during which time Leo interacts with a holographic recreation of Splinter. Splinter himself later appears in "Trans-Dimensional Turtles" when the Turtles and their 1987 counterparts travel to the Turtles' lair on Earth. This gives the Turtles the opportunity to bid farewell to Splinter, though Leo is unable to inform him that they are in fact from the future.
In "Earth's Last Stand" the events of "Annihilation Earth" are revisited, but the Turtles from the future arrive in time to warn Splinter of Shredder's attack. Splinter thus evades Shredder's strike and defeats him in a resulting duel, and the Earth is then saved by the efforts of the Fugitoid. A past version of Fugitoid then arrives to take the past Turtles, April, and Casey on an adventure, which-despite Splinter's initial misgivings-they willingly agree to, leaving only the set from the alternate timeline on Earth.
In "City at War," Splinter gladly promotes April to full "kunoichi" by presenting her with a tanto sword with the Hamato clan insignia. Upon hearing that her tanto was taken from her by a female witch-assassin, he assures April that failure is only possible when you give up.
In Episode 114, "Lone Rat and Cubs" how he get turned into a mutant-rat and took in the infant Ninja Turtles as his adopted sons, 15 years ago, is fully revealed.
2018 animated series.
In the 2018 Rise of the Teenage Mutant Ninja Turtles Splinter is Hamato Yoshi, his story is tied to mysticism and the Shredder, here a demonic suit of armor that consumed Oroku Saki, the man who first wore it.
The Hamato clan, founded by Oroku Karai, was started to protect the world from the possibility of the Shredder returning after he was banished to another dimension, called the Twilight Realm. 
Yoshis mother left when he was a child, to fulfill her destiny and watch to make sure the Shredder never returned. She left Yoshi to be raised by his Grandpa Sho. As he grew into a teenager Yoshi resented his Grandpa Sho and the destiny of the Hamato clan. He didn’t believe that there was a 500-year-old demon to watch for and resented the fact that it caused his mother to abandon him. Instead of learning how to defeat the demon Shredder, or use his Ninpo, magical abilities, he moved to America to make a name for himself in Hollywood.
In Hollywood, Hamato Yoshi adopted the stage name of Lou Jitsu and became an action movie star. As Lou Jitsu he was flashy, dated starlets, and had a good time, he continued to ignore any attempt from his Grandpa show to get him to leave Hollywood, and come back to Japan to fulfill his supposed destiny.
At some point, while an action movie star, he founded a chain of dojos, by the time of the series proper (30 years since he’s been back to one) there is only one left in the city. As seen in “Fists of Furry”
Eventually, Lou Jitsu fell in love with a woman and started dating her. On the day he proposed she revealed she was actually the yokai mob boss Big Mama, the proprietor of a yokai hotel, and the woman in charge of the Battle Nexus. Lou was kidnapped and forced to compete in the Battle Nexus, it is implied that most people who fight the Battle Nexus do not survive it. He was there for years, and while it seems everyone, even Splinter, recall the Battle Nexus as glory days, flashbacks show him as miserable and unhappy in his captivity. 
While trapped he eventually gave up fighting entirely and no longer would perform in the Battle Nexus or harm any living thing, but Big Mama would not let him go. He was broken out of his captivity by Baron Draxum, a yokai alchemist and warrior. Draxum believed that there was a threat to the secret yokai society from humans and sought to make warriors to fight for yokai. Draxum planned to use Lous DNA to mutate four turtles into warriors, since Lou was the greatest Battle Nexus champion ever. Lou, at first, made no move to stop or protest, until he saw the turtles that were to be molded into soldiers. He broke out of his captivity to spare them that fate, and in the ensuing escape was bitten by a rat he was also attempting to save and drenched in ooze. 
Yoshi abandoned his Lou Jitsu name and started going by Splinter sometime after escaping with the baby mutant turtles and set them up in a home in the sewer.
Splinter spent a lot of time watching Lou Jitsu movies in an attempt to relive his glory days, he did not focus on training the turtles as ninjas, since he didn’t believe in the demon Shredder there was no threat for the turtles to train for. After seeing the machination of the Foot Clan when he noticed April's new work uniform from The Foot Shack, a front for the Foot in the episode “Shadow of Evil” he finally came to believe the Shredder was indeed real & resolved to make sure the Foot could not summon him back.
However, in the episode “Endgame” when the Foot captured all four turtles he traded them the helmet of the Shredders armor for them, the last piece they needed to summon back the demon Shredder. Splinter and Leo obtained a collar to banish the Shredder again in “Many Unhappy Returns” Splinter and the turtles continued to have adventures until the Shredder returns, now under the control of the Foot, using a magical ring connected to the banishing collar. The turtles searched Splinter's memories to find a way to defeat the Shredder and summoned Karai back from the Twilight Zone. 
Shredder bore down on the lair and Splinter chose to remain behind to cover his son's escape from the Shredder. He was captured alive, with the intent to steal the innate magic he processed. The ritual was interrupted by the turtles, and after freeing Splinter they all worked together, with their ninpo, to destroy him for good.