All five were originally simply laboratory test subjects at Baxter Stockman's Stockgen corporation, a bioengineering firm in New York. Eventually a psychotropic drug that should give the cognitive characteristics of a person to an animal (or "splintering" the human-like cognition from the instinctual animal state, a term that Splinter owes his name) was tested on Splinter. When agents of the Foot Clan break into Stockgen and attempt to steal an alien mutagen, Splinter and the Turtles are also picked up, but manage to escape and are exposed to the mutagen in a sewer and grow into mutants. Splinter became aware of his former human life and of his treatment and began to teach his sons the art of Ninjutsu and of their old lives. While the element of Splinter being Hamato Yoshi is still present