Early in the 21st Century, THE TYRELL CORPORATION advanced robot evolution into the NEXUS phase - a being virtually identical to a human - known as a Replicant. The NEXUS 6 Replicants were superior in strength and agility, and at least equal in intelligence, to the genetic engineers who created them. Replicants were used Off-World as slave labor, in the hazardous exploration and colonization of other planets. After a bloody mutiny by a NEXUS 6 combat team in an Off-World colony, Replicants were declared illegal on earth - under penalty of death. Special police squads - BLADE RUNNER UNITS - had orders to shoot to kill, upon detection, any trespassing Replicant This was not called execution. It was called retirement.