If you're in the mood to start a serious Internet flame war, step into any science fiction forum, drop this question, then run away fast:
Is Deckard a human or a Replicant?
Movie geeks of all stripes have argued about whether or not Deckard is himself a Replicant, and at the end of the day, the movie never provides an answer. That means the debate fires can smolder for literally years. We have our own ideas to put out there, but you're never going to get a definitive answer.
The theatrical release seems to confirm that Deckard's birth didn't involve a bar code scan. Key scenes are cut and subtle clues simply don't show up. You can make the assumption that he's a Replicant, but there's not a lot of evidence to back you up.
However, with the various director's cut versions, the question gets a whole lot trickier, and some very tasty clues crop up to suggest that Deckard is also a product of the Tyrell Corporation.
Let's review the evidence;
1. Glowing eyes. At various points, Batty, Pris and Rachael all display weirdly glowing eyes, like raccoons in headlights. Human beings in the movie don't have that…except Deckard, who flashes them briefly after spending the night with Rachael.
2. Pretty, pretty people. Notice how the various real human beings in the movie are all physically damaged in some way? Gaffe has a limp. Sebastian has an accelerated aging disease. Tyrell's wearing glasses the size of an industrial mixer. And Bryant? We're pretty sure Bryant just oozes Crisco oil out of his pores. (It's suggested, though not stated, that all the pretty people have decamped to the off-world colonies, leaving Earth for the ugly kids to inhabit.)
Now look at the Replicants. They've got it going on: strong, healthy, launching back-kicks at the drop of a hand, and generally vamping it up like supermodels when they aren't finding people's eyes to punch in. There's a pretty clear distinction between human and Replicant…
…except for Deckard, played by Harrison Ford in his Maximum Hunk era and looking good enough to eat with a spoon. Hmmm…
3. The Unicorn. The biggest piece of evidence in the "Deckard's-a-Replicant" theory comes at the end, when he discovers Gaffe's origami unicorn lurking outside his apartment. Why is this important? (You know, besides the fact that Gaffe was there and didn't fill Rachael with more holes than a whiffle ball?) Because earlier in the film, Deckard had experienced a dream about a unicorn. That suggests that Gaffe knows something about Deckard's dreams, which further suggests that those dreams are factory standard.
4. The director says so. Did we mention the biggest piece of evidence? We forgot the part where Ridley Scott ruins everyone's fun by coming out and straight-up stating that Deckard is a Replicant. Way to kill those Internet flame wars, Ridley.