Dragonlord

Dragonlord is the main villain of the original Dragon Quest (sometimes called Dragon Warrior) - he stole the mystical Ball of Light in order to flood the world with demons and monsters while also kidnapping Princess Gwaelin for unknown reasons.

Although he appears as a wizard for the majority of the game his true form is revealed to be a large purple dragon - which is probably where his name, as well as the name of the series, derives from.