Robot

Robots are mechanical or synthetic beings that usually inhabit continua when there's technology involved. They even exist in the Real World.

Depending on their designs and functions, they are the most diverse beings of the multiverse, rivaling humans. They also vary in intelligence: they could be mindless drones, average-minded sentients, or even go beyond genius level. Most of them are made of metal, but others can be built with artificial materials such as plastic.

Robots are not to be confused with AIs, although many robots may possess artificial intelligence.

Types of Robot
Generally speaking, robots fall into one of two categories: 1. your basic mechanical robot, and 2. androids.

Robots
The term "robot" can be used generally for all mechanical beings, but when applied specifically it refers only to those that are distinctly mechanical and non-humanoid (or so obviously mechanical that being human-shaped doesn't matter). Robots are often of sub-human intelligence, but not always.

Robots in Canon

 * Centurions (Battlestar Galactica)
 * Crow T. Robot and Tom Servo (MST3K)
 * DRDs (Farscape)
 * The "fix-its" (*batteries not included)
 * GERTY (Moon)
 * K-9 (Doctor Who)
 * Roombas (Real World)
 * Sentinels (X-Men)
 * Transformers (Transformers)
 * Wall-E (Wall-E)
 * Isaac Asimov's robots (I, Robot series)
 * Most bots (Futurama)
 * Most droids (Star Wars)
 * Haros (Most Gundam Continua)
 * Marvin (The Hitchhiker's Guide to the Galaxy)
 * Mecha Koopas (Mario)
 * Robotic Operating Buddy (Super Smash Bros. Brawl, Real World)
 * Necrons (Warhammer 40,000)
 * Robot Masters, Reploids, Mechaniloids, and Reaverbots (Mega Man Series)
 * Geth (Mass Effect)

Androids
The term "android" refers specifically to mechanical or synthetic beings designed to look and act human. This description is often the cause for lots of moral and/or ethical drama in their home continua.

Androids in Canon

 * Ash (Alien)
 * Data (Star Trek: The Next Generation)
 * Erek King (Animorphs)
 * Replicants (Blade Runner)
 * "Skin-job" Cylons (Battlestar Galactica)
 * T-800 and T-1000 (The Terminator series)

The Three Laws of Robotics
Isaac Asimov's positronic robots were all programmed to obey three laws. Since Asimov's time, the Three Laws have become such a well-known concept in science fiction that it is almost impossible to talk about robots without someone bringing them up. They are as follows:

A Zeroth Law was later added that took precedence over the first three, as well as a Fourth Law that allowed for free will within limits:
 * 1) A robot may not injure a human being or, through inaction, allow a human being to come to harm.
 * 2) A robot must obey any orders given to it by human beings, except where such orders would conflict with the First Law.
 * 3) A robot must protect its own existence as long as such protection does not conflict with the First or Second Law.

0. A robot may not injure humanity as a whole or, through inaction, allow humanity to come to harm.

4. A robot may do whatever it wishes as long as its actions do not conflict with any of the other Laws.

Unfortunately, the Three Laws are not foolproof. When robots start interpreting the Zeroth Law to mean that humans must be protected from themselves, they start trying to take over the world. This is generally seen as a bad thing. Also, some robots in some continua never use these laws at all, such as the droids in Star Wars.