Slash is a fictional character in Teenage Mutant Ninja Turtles. In the series, he was introduced pet box turtle, who used to listen to his owner's angry ranting about his troubles with his family for the majority of his life, and also learned ninjutsu by watching Raphael practice in his room. Although no one knew at the time, Spike developed a hatred for the other Turtles, especially Leonardo, who Raphael was at odds with the most, thanks to hearing only Raphael's angry, one-sided rants all his life.. Raphael loved Spike and protected him with his life, often being most concerned about him when danger is about. In Slash and Destroy, Spike drinks from a jar of mutagen, mutating into a towering, hulking mutant turtle. When Raphael discovers him, Spike offers to become his new partner, so they can take on the Kraang on their own terms, which worked out very well. Spike also renames himself Slash, and comes to wield a giant mace in battle. To Raphael's horror, however, Slash ferociously beats down Donatello and Michelangelo, believing Raphael doesn't need them. Slash's murderous spree nearly claims Leonardo's life, until Raphael finally confronts him, calling him a "freak". Hurt and angered, Slash engages

Slash is later seen being kept as a prisoner of the Kraang in Metalhead Rewired. When Metalhead frees him and the other captured mutants, he takes part in the battle to ensure everyone's escape. During the fight, he saves Raphael from a Kraang and respectfully nods before fleeing back to New York. Slash would end up captured again in Newtralized, but is saved by the Newtralizer. Slash pledges his brotherhood to the Newtralizer, and together they embark on a violent but effective crusade against the Kraang. However, it's revealed that Slash, in spite of his dislike of the other turtles, still shares the same beliefs they were taught regarding the protection of the innocent (though is much more brash and violent about his methods), showing him to be more of an anti-hero who genuinely wants to defeat the Kraang and save humanity. This puts him at odds with the amoral Newtralizer, who is prepared to destroy New York and kill all humans to defeat the Kraang, pressuring Slash to help him since they are "brothers". Realizing the position he put Raphael in, he ends up siding with the Turtles against the Newtralizer, who tries to destroy them all. The Newtralizer is defeated, and Slash makes amends with Raphael, but respectfully declines his offer to rejoin the Turtles before departing. In the season finale, Raphael expresses concern regarding Slash's status during the Kraang invasion of New York.

Slash made his return in Battle for New York, where he leads the Mighty Mutanimals, consisting of Leatherhead as the 2nd in command, Tyler Rockwell the brains, and Piegon Pete the spy/decoy. He was first seen fighting the Kraang that were pursuing the turtles. Despite both Raph and Mikey's support Leo is shown to distrust him, considering the last encounters they fought. However, with counsel from Jack Krutzman and Splinter, the two were able to overcome their differences and work together to stop the Kraang from mutating Earth and saving New York's citizen trapped in Dimension X. Slash explains that since his mutation, his mind has become much more stable; in other words, the mutagen had affected his mind, leaving him one-tracked. He told an impressed Leonardo that he tried to model himself after the best leader he knew-Leo himself.

The Mutanimals confronted Tiger Claw in Clash of the Mutanimals, but were easily defeated by the Shredder's lieutenant. Slash and Rockwell would be taken back to the Foot's headquarters, where Baxter Stockman administered a worm embedded with his experimental mind control serum. Slash and Rockwell were turned into sleeper agents that were rescued by their friends, but viciously attacked them once they were brought to the Turtles' lair. The two kidnapped Raphael and had him turned into a sleeper agent as well, but the Turtles, Leatherhead, and Pete were able to free the three from the Shredder's control. All eight mutants then assaulted Shredder, and Slash defeated him by crushing him under a statue before the group retreated. Slash then made amends with Splinter, who he had earlier attacked while under the Shredder's control.

In "Dinosaurs Seen In Sewers", while on the trail of a supposed "dino-man" in the sewers, Slash and Rockwell encountered the genuine article: a crazed, alien Triceraton scout named Zog. Slash and Rockwell were quickly subdued by the alien, and Rockwell warned the Turtles about Zog's presence in the sewers before getting the two of them to the lair, where they healed from their injuries. They recover enough to join the battle against the Triceraton Empire in the season finale "Annihilation: Earth", alongside many of the Hamato Clan's allies, but their combined might is still no match for the alien invasion. Slash is captured by the Triceratons and ends up being sucked into the black hole that destroys Earth, killing him. However, Professor Honeycutt rescued the Turtles from this event and then traveled back in time to six months earlier in order to prevent it from occurring. Ultimately, the Turtles are able to change the timeline and save Slash and the rest of the world in "Earth's Last Stand".

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