Roy Batty, left, meets his 'maker,' Dr. Eldon Tyrell, in Tyrell's apartment. Batty, a Nexus-6 replicant, was seeking more life from Tyrell, who engineered this model to have a short lifespan.
Nexus-6 is a series of Replicants said to have been made for superior strength and agility, for use in off-world mining colonies.
In Blade Runner, the Nexus series of replicants – genetically engineered by the Tyrell Corporation – are virtually identical to an adult human being, but have superior strength, agility, a wider temperature range tolerance, and variable intelligence depending on the model.
Because of their physical similarity to humans a replicant must be detected by its lack of emotional responses and empathy to questions posed in a Voight-Kampff machine test. A derogatory term for replicant is "skin-job" (in the original release, the Deckard voiceover explicitly states this--in the subsequent releases without the voiceover, the viewer must infer this).
As of 2019, the latest model of replicant is almost indistinguishable from humans. In fact, the Tyrell Corporation advertises this model as "More human than human." If replicants are given memories (and thus think that they are indeed human), the VK test almost fails- It takes over a hundred questions to expose the replicant known as Rachel.