Robots play a very interesting role in Foundation (or should I say played a very interesting role). In the beginning of space colonization, many years before the Foundation series, robots were a common thing. They even played a part in the fight between the earliest colonized worlds and earth. But, sometime after the era of colonization, they mysteriously faded away into the background.

In the preqeul to the original Foundation trilogy, Prelude to Foundation, the robot, Daneel (who existed since the beginning of the colonization era) helps Hari Seldon through the process of creating psychohistory. This robot is doing this because he is programmed to help humankind in any way. He also plants the seed for Gaia, which is an alternative to the Foundation. In the last book in the Foundation series, this same robot leads Golan Trevize to the planet of earth, where he finds the reason that Gaia is a better choice than psychohistory (as explained in the future of Foundation). Trevize also helps Daneel transfer himself into the body of Fallom, part of a species of genetically engineered, hermaphroditic, and transductive humans. He does this because his "brain" has become too condensed to be miniaturized any longer without coming up against the uncertainty principle (a law that states that by simply measuring something smaller than an atom, we disrupt the system). If he made his brain any more complex, it would become very unstable and deteriorate much more quickly (remember, this brain is a robotic one). This allows him to guide humanity through the process of becoming a massmind for the few hundred years that this new body allows. (See the future of Foundation for details on why this is a good thing).