John Isidore lives by himself in a San Francisco apartment. Not just a single apartment, mind you. He is the only one living in the entire apartment building, which means life is pretty lonely existence until one day, he gets a new neighbor. Hooray! What's more, the neighbor, Pris Stratton, is a bona fide human girl.
Well, except for the "human" part.
He's a genetically degraded human being with a heart of gold; she's an escapee android with the social skills of a gorgon who has bad breath. Sure, sure, it sounds like a pitch for some weird future sitcom but nope. It's actually kind of sad.
If Isidore were a superhero, he'd be Empathy Man. Sure, he doesn't get the most exciting powers, his alter-ego name could use some rebranding, and it won't take an army of computer animators to render his exploits on the silver screen. But he might be the most useful superhero in the end.
As empathy man, Isidore is a foil for Rick—that is, the differences between him and Rick highlight Rick's key characteristics. As Rick's foil, Isidore has several traits that Rick will adopt during his life-altering day, and empathy is the most crucial. Honed by his use of the empathy box, Isidore has empathy for all living things, including androids. We get a hint of this during Isidore's day at work when he accidently brings a real cat in, believing it to be electric:
"I don't think Isidore can tell the difference," Milt said mildly. "To him they're all alive, false animals included. He probably tried to save it."
Milt points out an important aspect of Isidore's character: if a creature is in pain or needs help, artificial or organic, Isidore will try to help it. He is so equal in his worldview that he can't even tell the difference. This life-blindness extends to the androids that come into his care as well, first Pris and then Irmgard and Bay. While most people in this society put themselves above the androids, Isidore sees himself on the same level as them:
"That's right, Mr. Baty," Isidore said. "But what does it matter to me? I mean, I'm a special; they don't treat me very well either, like for instance I can't emigrate." (14.78).
Even after watching the androids torture the spider, Isidore refuses to help Rick find them in the apartment building. He tells Rick he's looking after them and even warns Rick that if he kills them he "'won't be able to fuse with Mercer again'" (19.20).
Stuck between the killer and the prey, Isidore sympathizes—or empathizes—with both.
Isidore is the type of person they call a "special" in the future. And no, that's not the good kind of special. (Is there a good kind of special anymore?) During our introduction to the character, we learn this:
He had been a special now for over a year, and not merely in regard to the distorted genes which he carried. Worse still, he had failed to pass the minimum mental faculties test, which made him in popular parlance a chickenhead. (2.13)
Isidore may lack when it comes to an IQ test, but he has an innate knowledge of the world around him that makes almost savant-like. Like, he notices that Buster Friendly and Mercer are in competition with each other before Buster Friendly's expose (7.30). He also notices the androids are androids simply by observing them.
Watching them interact, Isidore thinks: "[T]hey're all strange. He sensed it without being able to finger it. As if a peculiar and malign abstractness pervaded their mental processes" (14.21). He doesn't know they are androids, but at the same time, he knows, you know?
Isidore's distorted genetics also affects his place in society. Here's a little briefer on the standards of the future society:
Loitering on Earth potentially meant finding oneself abruptly classed as biologically unacceptable, a menace to the pristine heredity of the race. Once pegged as special, a citizen, even if accepting sterilization, dropped out of history. [Isidore] ceased, in effect, to be part of mankind. (2.5)
As a chickenhead, Isidore has been dehumanized in much the same way the androids have. He's considered less than human, which is super ironic: if any character could pass a Voigt-Kampff test, it's Isidore. The guy has empathy to spare.
Although desperate to live within a community, Isidore is forced to live the isolated life of an android. Thanks to Isidore, we learn that there's actually nothing wrong with androids, or with special—there's something wrong with society, man.