The Nexus series of replicants – genetically engineered by the Tyrell Corporation – were virtually identical to a human being. Marketed as being "more human than human," the Nexus-6 had superior strength, agility, a wider temperature range tolerance, and variable intelligence depending on the model for use in Off-world mining colonies.
Because of their physical similarity to humans, a replicant could only be detected by anomalies in bodily responses to emotionally charged and sometimes disturbing questions during a Voight-Kampff test.
The Nexus-6 line had a limited lifespan, lasting just four years. Batty and the other replicants returned to Earth to seek more life, but Tyrell said he was unable to alter the genetic make-up of the series.
Batty was perhaps the most perfect of this series, and the one who led a rebellion of replicants back to Earth. He said he had done "Questionable things." His creator, Tyrell, replied that he had done "extraordinary things."
As he sat dying with Deckard on a rooftop, Batty said stated the uniqueness of the Nexus-6 series and their ability to go where no humans had gone, and do things no human had done.
- "I've seen things you people wouldn't believe. Attack ships on fire off the shoulder of Orion; I watched C-beams glitter in the dark near the Tannhäuser Gate. All those moments will be lost in time like tears in rain."