The Grineer are clones to a man; products of ancient, half-remembered technology. Grineer soldiers are produced in industrial quantities. They are all genetically defective, their genome damaged by the invasive cloning procedures used to birth each generation century after century. As a result, they have a life cycle that is limited only to a fraction of a normal lifespan. Indeed, it could be argued that the Grineer are better at fixing broken bodies than they are at making ones that function to begin with. Their homeworld is a ruined, barely habitable Earth. They are people acting on an ultimate xenophobia, fueled by hereditary madness, and a burning hate of anything and anyone not like themselves. In the end, should they succeed, there will only be Grineer left alive in the Origin System