Hamato Yoshi

Hamato Yoshi in all continuities, was once a great and honourable ninja whose story is always closely intertwined with that of Splinter. He is almost always dead when the story starts.

In most versions he was the owner of a pet rat who became Splinter; this includes the original comics and Teenage Mutant Ninja Turtles 2003 cartoon series. The earlier 1987 cartoon series (along with the Teenage Mutant Ninja Turtles Adventures comics) provided a twist in that Hamato Yoshi was Splinter, having been turned into a giant rat.

Eastman and Laird's TMNT
In the comics, Hamato Yoshi is a highly-ranked member of the Foot Clan in Japan. Splinter is his pet, who copies him as he practices Ninjutsu. When he got romantically involved with Tang Shen, he invoked the jealousy of Oroku Nagi, who also loved Shen. When Nagi got enraged with jealousy, Yoshi was forced to kill him to protect Shen. Dishonored for having killed another member of the clan, Yoshi was forced to choose between exile and death. He choose exile and moved to New York City with Shen. Years later, Oroku Nagi's brother, Oroku Saki killed them both to avenge Nagi. Splinter escaped to the sewers, where he and the Turtles were mutated. He taught them Ninjutsu in order to avenge the death of Hamato Yoshi.

In Tales of TMNT #22, the Turtles encounter a female ninja with a Shredder gauntlet. She vows to kill the Turtles for crimes Hamato Yoshi committed against her family.

1987 Series and Archie Comics
Like in the earlier comics, Hamato Yoshi was a member of the Foot Clan. However, Oroku Saki frames Hamato Yoshi for plotting to kill of one of the Foot's Clan leaders. Yoshi is exiled to New York City, where he is forced to live in the sewers and befriend the rats. Years later, when Saki moved to New York himself, he dumps the mutagen into the sewers to kill Yoshi. However, the mutagen mutates Yoshi and his four pet turtles. Yoshi turns into a giant rat, the last animal he was in contact with, and takes on the name Splinter, a nickname the Turtles gave him.

The Archie comics gave more backstory to Hamato Yoshi when he, the Turtles and April visited Japan. He recounted his youth training under his Uncle Giyogi near the outskirts of Hiroshima, and personally saw the devastation of the city after the atomic bomb was deployed.

Movies
Yoshi's story, explained in the first movie mirrors the story of the original comic books, except Oroku Nagi is removed from the story and the conflict is with Oroku Saki himself rather than Oroku Nagi. Instead of fleeing the clan because of a murder of a clan member, Tang Shen persuades Yoshi to flee to America in order to avoid dueling Saki, (presumably to the death) for her hand in marriage. Saki vows vengeance and spent years searching for them. Saki eventually finds and kills both Yoshi and Shen in their New York apartment, leaving Yoshi's pet rat Splinter homeless. The actor who portrayed 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, Michaelangelo 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 number of past incarnations of other characters that the turtles meet on this adventure (such as a British ancestor of Casey Jones, Whit) a direct relationship between this boy and Hamato Yoshi seems implied. If this is indeed the case, then when the turtles save the boy's life, they are also saving their own future, as their origin is inexorably tied to the fate of Hamato Yoshi.

2003 Series
Hamato Yoshi's story has been fully revised in this version. The story is revealed in A Tale of Master Yoshi.

Hamato Yoshi was an orphan, living in the streets of Japan with his best friend, Yukio Mashimi, in the 1960s. When Yoshi returned a 5-yen coin dropped by the Ancient One, he took them in for their honesty, raised them as his sons, and taught them Ninjutsu. They both fell in love with Tang Shen, another orphan taken in by the Ancient One. Shen loved Yoshi more. During this time, Shen found a rat in the house and kept him as a pet.

One night, Yoshi, Shen, and Mashimi saw a lone man being attacked by four ninjas. Yoshi and Mashimi decided to help the man and fought off the ninjas. The man was actually the Utrom Mortu and the ninjas were members of the Foot Clan. Impressed by their skill and already having his secret revealed due to battle damage, Martu offered to make the two Guardians. They accepted, despite their master's objections.

As a Guardian, Yoshi seemed to advance continually, while Mashimi never seemed to get anywhere. In anger, he murdered Tang Shen and betrayed the Utroms to The Shredder. Yoshi and the Utroms escaped. Soon after, he discovered Tang Shen dead. In anger, Yoshi stormed the Foot's citadel and killed Mashimi in single combat.

With their Tokyo base discovered, the Utrom set up a new base in New York under the name T.C.R.I.. Yoshi went with them, taking Shen's rat with him. He named the rat Splinter to remind him of the splinters of anger and hate that drove him to kill Mashimi.

However, the Shredder followed Yoshi and tried to force him to reveal the location of the Utroms. Yoshi resisted and was killed. Splinter escaped to the sewers, where he mutated along with the Turtles. He proceed to teach them Ninjutsu, just as he had learned from Yoshi.

Yoshi was also a champion of the Battle Nexus.

Ninja Tribunal
It's revealed in The Lost Episodes that Yoshi and the Utrom tried to get the Ninja Tribunal's help in the fight against the Utrom Shredder, warning them that the alien may challenge the evil one. Due to their refusal to help, Splinter partially blames them for Yoshi's death.

When the Tengu Shredder goes to attack Splinter, Hamato Yoshi manifested from the Turtles' medallions. He snatches the Shredder's trident and then slashes him with it, causing precious energy to leak from his armor. When the Tengu Shredder was on the verge of defeat, Yoshi manifests himself through the Turtles' medallions again, which shatters them and then he slayed the demon by slicing him in half.

Video Games
When you beat the very first video game Splinter turns back into Yoshi. Yoshi is an unlockable playable character in the 2003 video game.