'Blade Runner: Do Androids Dream of Electric Sheep?' (1968) by Philip K Dick

The novel is set in a post-apocalyptic San Francisco, where Earth's life has been greatly damaged by a nuclear global war, leaving most animal species endangered or extinct. The main plot follows Rick Deckard, a bounty hunter who has to "retire" (i.e. kill) six escaped Nexus-6 model androids, while a secondary plot follows John Isidore, a man of sub-par IQ who aids the fugitive androids.