An avatar is the human form that a Dragon, Unicorn or some other awesome creature can take when they reach maturity. Grandpa Sorenson mentioned this to Kendra before she met the sphinx for the first time in The Rise of the Evening Star. Some believed that the Sphinx was and actual Sphinx that had taken on the form of a man. The avatar of a creature is said to be the perfect disguise by Gavin(Navarog) to Kendra in The Secrets of the Dragon Sanctuary. This form is almost impossible to distinguish from a regular human. The avatar of a creature is (almost) always human with the notable exception of Raxtus.