Masahiro Mori, “The Uncanny Valley” (1970)

Mori was a roboticist who wrote "The Uncanny Valley." This short essay explains a phenomenon in which there is a certain point where a robot who looks human begins to give off a sense of eeriness. They are not comletely human-like and not completely robot-like, thus straying away from the familiar. He warns designers that there is a danger of dipping into the uncanny valley the more human-like we try to make a robot in appearance. Though there is a chance of success, it is at a great risk of the robot becoming unfamiliar instead.  

Mori's work has been noted in many works, some people criticizing others' creations such as the cgi film The Polar Express as being creepy because of the animated children. These children looked so close to human, but they definitely were not. Freud in his work "The Uncanny" states that this phenomenon happens because the familiar, the things we see from day to day, become unfamiliar and instills a sort of fear. 

Sources:

Freud's "The Uncanny"

Mori's "The Uncanny Valley"

Article on why Polar Express is creepy