Kunzig – Rick Deckard in Blade Runner vs. Rick Deckard in Do Androids Dream of Electric Sheep

There are many ways in which Blade Runner's interpretation of Philip Dick's Rick Deckard differs from the original. To start with, Scott basically inverted Deckard's basic background information: in the book, Rick Deckard is married, and currently employed as a cop, more specifically a bounty hunter. In the movie however, Deckard is divorced, as we learn through the voice over, and he is an ex-cop, no longer a bounty hunter. These are two basic, obvious characteristics that separate them; but there are some more important ones that make a bigger difference in the character.
The first is that Dick's Rick Deckard seems to only be a mediocre bounty hunter. He is only given the cases that Holden, the senior bounty hunter, believes he can handle. The only reason he is assigned to the specific escaped androids the story centers around is that Holden was shot by one of them, was hospitalized and therefore unable to complete the mission. But since they represented more of a challenge, Holden had planned on taking care of them himself.
In the movie however, Rick Deckard is presented as the best blade runner (or bounty hunter), pulled out of retirement to work his magic by his old boss, because Holden was unable to handle the replicants. Holden got the first shot at them only because he still worked as a blade runner, whereas Deckard had quit.
The second important difference is that the book's Deckard wants to be assigned to more cases, because he gets payed for every android he retires, and he needs the money, specifically so he can purchase a real animal. Blade Runner Deckard does not wish to do this job, but his boss doesn't give him a choice, threatening him.
A third important difference, revealed to us as were the others within the first 20 minutes of the film, is in the attitude each Deckard has towards the job. In the beginning of the book, Rick Deckard doesn't appear to particularly mind his job – he is simply retiring androids, and doesn't start to think of it as killing until much later. But from the beginning of the movie, Deckard dislikes retiring the replicants, because he already sees it as killing, which is why he quit.
I think a main way in which they are alike is that they are both lonely. Even though Dick's Deckard is married, him and his wife don't always connect that much, and most of the time he seems to be alienated from whomever he is with, as does Deckard in the movie. But they both experience a change – Dick's Deckard begins to feel empathy for androids when the opera singer is killed, and Scott's Deckard begins to feel empathy for replicants (more specifically for Rachel) when he realizes they might actually have feelings. And both Deckards develop a soft spot for Rachel despite themselves.