Demon/History

Mintwallin spawn
The first demon spawned in Mintwallin, south of the current city, and was a lot weaker than today. It disappeared in a 1999 or 2000 update. It looked a bit different:

Demons are brought back to Tibia
When Edron was introduced, the Demons could be found and killed again, this time only for people with a Premium Account. They received a new outfit, the one they currently use.

No longer strongest normal creature
The christmas 2006 update brought new demonic creatures to Tibia, among them the Juggernaut which is stronger than the Demon.