^InMulligan, Jessica; Patrovsky, Bridgette. Developing online games: an insider's guide. New Riders. 2003., Randy Farmer is quoted (p.454): "It is important to realize that the term 'avatar' was used in another game later [??] in that period (Ultima IV) and that the concept of an 'avatar' was in several works of fiction prior to the development of Habitat including Vernor Vinge's True Names and John Brunner's Shockwave Rider."
^Jordan, Tim. Cyberpower: The Culture and Politics of Cyberspace and the Internet. Routledge, 1999. ISBN 0-415-17078-8