Why is Satan called the dragon and beast. Is it his appearance? Did his appearance naturally change after he rebelled? Also how did fallen angels and demons change in appearance?
Satan gets the name dragon from a vision John recorded in Rev. 12. He is specifically mentioned in Rev. 12:3 and his identity is confirmed in Rev. 12:9.
The beast is actually a name for the anti-Christ and comes from Rev. 13. These are both symbolic names and aren’t meant to describe their physical appearance.
According to Jude 1:6 and Genesis 6:4 fallen angels abandoned their original form and became physical beings which allowed them to produce offspring with human women. Some believe demons are the disembodied spirits of those offspring, called nephilim in Genesis 6:4. If so, they began as physical beings and are now spirits.