What properties does a robot have?
There really is not a total consensus in the properties that robots have. There are some actions that allow people to define a machine as a robot or not. One of the most important properties is that it is artificially created. If it is a biological entity, it cannot be considered a robot. Other properties are that the robots must be programmable, be able to sense its environment and interact independently. It also has to serve a purpose. You might be surprised but actually resembling a human is not one of the properties. Robotic engineers are more focused on the controlled actions than it appearing humanoid.
Is there a sentient robot in existence?
Whether or not there is an actual "sentient" robot in existence is all depending on how you view sentience. There are robots that look very human and can perform many functions. At this point it is more about the robots being intelligent machines. Many can actually have the ability to sense its environment and can move without direct human intervention.
One of the requirements of being labeled as "robots" is that it has to have the ability to make some choices on its own. Mechanized devices that cannot meet some of these criteria set forth are simply referred to as machines. It is important to note that robots do not have to be humanoid in appearance though. If the measure of sentience is by making logical choices and the ability to think independently...there are certainly sentient robots in existence.
What role has robots played in literature?
This may come as a shock to you but the first reference to mechanical servants is from Homer's Iliad. In it Hephaestus is helped by human-like mechanical devices to create new armor for Achilles. But it was not until the writer Isaac Asimov that the robot really came to be a staple in Science Fiction. It was Asimov that created the Three Laws of Robotics that many writers refer to even to this day in literature and film.
