Be it as small as a false name or as large as a 3D image with a business card and background history. Some interesting work on avatars and multiple personality is being done at Univ of Texas ACTlab. You mentioned in your short bio that biota.org is promoting the idea of artificial life forms. An avatar is an incarnation of a person. Biota.org is nothing directly to do with avatars.
Avatars are the form in which humans appear in virtual worlds.
But a world with only humans and pre-programmed bots is not such an interesting place. The real world is fun because of the unexpected and the beauties of nature. So these biota would co-exist with humans in some virtual worlds. But in many worlds they would just exist for themselves. Humans could watch them but not necessarily interact with them.