Slash is an anthropomorphic snapping turtle that appears in 2 TMNT incarnations; the first animated series and Archie comic book series. In both continuities he is at some point been at odds with the turtles, and is obsessed with Palm Trees.
1987 Series
In the animated series, he was a mutant turtle, created by Bebop and Rocksteady to do chores Shredder had assigned that they didn't want to do. In this incarnation his obsession with palm trees was in particularly focused on the plastic tree in his bowl before mutated.
Archie Comics
In the Archie series, Slash was merely an alien that happened to be an anthropomorphic snapping turtle. Originally he lived on a world filled with lush palm trees. Slash's paradise would be shattered when invaders came and cut down all of his his precious trees. Slash soon came across the banished Krang and made a deal to help him back to earth. Under Krangs leadership Slash teamed with Bellybomb and fought the turtles while Krang sought a new body...that of Shredders.
Later in the series, Slash went on a rampage which drew the attention of the Mutanimals. After he was captured and imprisoned the Mutanimals broke him out and took him back to their island. Once awakened Slash continued his violent spree until subdued by Leatherhead. Now in a somewhat more peacefull state, the Mutanimals were able to calm him enough to inform him that he would be allowed to stay in a grove of lush palm trees he so loved. A greatfull Slash strode off happily and would become an ally of his rescuers.
Later, Slash sacrificed himself to save the TMNT, Ninjara, and their future counterparts from a fiery death aboard a spacecraft that was hurled toward the sun.