The serpent
The serpent, in his Edenic form, is not to be thought of as a writhing reptile. That is the effect of the curse (Genesis 3:14). The creature which lent itself to Satan may well have been the most beautiful as was the most "subtle" of creatures less than man. Traces of that beauty remain despite the curse. Every movement of a serpent is graceful, and many species are beautifully coloured. In the serpent, Satan first appeared as "an angel of light" (2 Corinthians 11:14).