I want to make a short comment about “The Media Equation” from Reeves and Nass* since it has many implications for the design of artificial creatures.
Their theory claims that humans are social animals that come from their evolution history: they interact following the rules of interpersonal communication even if the interaction is not with a person (anthropomorphism). In other words, they tend to respond to media as they would another person like by being polite, cooperative, and attributing a personality type.
*Byron Reeves & Clifford Nass, The Media Equation: How People Treat Computers, Television, and New Media like Real People and Places, Cambridge University Press (1996).
More precisely, the media equation relies on eight main propositions:
(1) Everyone responds socially and naturally to media.
(2) Media are more similar than different.
(3) Reactions occur automatically without conscious effort.
(4) When using any type of media, a person is likely to assign it a personality.
(5) What seems true is more important than what is true.
(6) People respond to what is present.
(7) People like simplicity.
(8) People already know how to function in the natural world (be polite, etc.).
From my experience, I think this is also true for artificial creatures. It appears to me that the Media Equation is a good guide for creating interacting characters. It does not contain all the rules, but these ones are important.