The Doctor usually takes other people with them, who are usually called "companions" or "assistants". The Doctor and their companions travel through space and time, have a lot of adventures, and often save many people. The character of the companion was there so that the people watching the series could identify and feel close to a character. The companions were often present-time humans, so people could feel close to them, and they knew as much as the viewers. Because of this, the Doctor could explain things to their companions, and at the same time to the viewers. Almost all the Doctor's companions have been human, or human-looking aliens. Two companions were robots.