The genetic template of the S-Gray aliens comes from the legendary Grays (or Greys), which have captured the imagination of the public since the alleged abduction of the Betty and Barney Hill couple. In the 2003 series these aliens were shot down in Roswell by xenophobic government agents lead by Agent Bishop and conserved in the research laboratories of the Earth Protection Force. Genetic information of the Grays - just like a number of other aliens, who had the misfortune to be captured by the Earth Protection Force - was used by Bishop to create an army of super soldiers, which in the case of an alien invasion would form the main line of defense of the earth. When the President of the United States, who held supreme authority over the Earth Protection Force, which wanted money, wanted to cut the EPF's funding, because it appeared the organization was useless, Bishop unscrupulously used the results of his work to simulate an Alien invasion and thus to make the President gave the EPF unlimited money. To this end, Bishop let Baxter Stockman produce a series of alien clones whose genetic template consisted of a mixture of various alien DNA and which were remotely controlled by a computer program (without this signal the S-Grays were nothing more than idle, mindless shells). The Turtles who accidentally stumbled on this plan, tried their best to thwart Bishops intentions, but failed, and so the EPF continued to receive the support of the government.
However, the genetic mixture, composed of the S-Grays, was extremely fickle and easily led to self-destruction of the S-Grays once they took a powerful hit. Apparently, Raphael likes watching them "go pop". After the fake alien attack street cleaning caused the genetic mash to be simply flushed into the New York City sewer system. However, this substance proved to be so aggressive that it mutated any living thing that came into contact with it, which later had serious consequences for the safety of the city.