The Slayers were clones created by John Bishop. Their purpose: was to create a new humanity, a new superior race born of enhanced DNA; DNA acquired from genetic manipulation, alien autopsies, and even stole from the Ninja Turtles. But it was Splinter's mutated rat DNA being so nearly human that had allowed Bishop to finally complete the process.
Bishop planned to make them future members of the Earth Protection Force. By cellular acceleration, Bishop could give birth to an army within 6 hours fully trained thanks to his advances in bio data transference and Splinter's DNA. Bishop planned to mainstream them into the population. The Slayers goal was to fare aliens out.
When the Ninja Turtles came to rescue their master Bishop sent a prototype slayer out to fight them. However thanks to the help of Honeycutt, Leonardo managed to trap the Slayer in a preservation tank. When Splinter overloaded Bishop's computer, Bishop's lab was destroyed along with his Slayer program. Save for the prototype who was washed away.