The Final Boss of the very first Dragon Quest game is the Dragonlord. Before the game starts, he stole the Ball of Light to conceal the kingdom of Alefgard in a veil of darkness. That all came to an end when the descendant of Erdrick came to Dragonlord's Castle and defeated him in battle.
The Final Boss of II is Malroth. After the death of the evil priest Hargon, this God of Destruction rises to finish off the Heroes and make sure evil conquers all.
The postgame content of Dragon Quest II HD-2D Remake introduces a "true ending" in which Malroth fuses with the lingering spirit of Calasmos to become Malwrath, the "true final boss."
The Final Boss of III is Zoma. Having traveled to Alefgard after the defeat of the Baramos, the party confronts his master and vanquish with the Sphere of Light, thus setting the stage for the other games in the Erdrick trilogy. First introduced the Disruptive Wave technique.
The Final Boss of Dragon Quest IV is Psaro the Manslayer. The demonic transformation of the game's main villain, Psaro, he sought to unleash the power of the Secret of Evolution as the Master of Monsters. Distinctive for having a total of seven forms in the battle, the most in the series by far.
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The Final Boss in V is Grandmaster Nimzo. He is known as the lord of evil and has imprisoned Madason's mother, Madalena in Nadiria, waiting for the Legendary Hero to arrive.
The Final Boss in VI is Mortamor. After two confrontations with the party in separate forms, the Demon King sheds his body apart and attacks with his (disembodied) head and hands. However, even after becoming more powerful, Mortamor is still no match for the Hero and his party. Everyone soon rejoices the heroes' victory over the evil Devil Lord. An alternative ending happens when Nokturnus instead defeats Mortamor. This only happens when you defeat Nokturnus under twenty turns.
The Final Boss in VII is Orgodemir. After being revealed for impersonating The Almighty, the Fiendlord escapes into the Cathedral of Blight awaiting his enemies in the throne room. Upon his ultimate defeat, Orgodemir curses The Almighty and all those who follow him and disintegrates.
The Final Boss in VIII is Lord Rhapthorne. After his first defeat, Rhapthorne absorbs the entire Black Citadel, and transforms into a stronger being: a large, bloated devil looming over the land. However, his reign of terror wouldn't live long enough as he is defeated by the party, riding on Empyrea's back.
The Final Boss in IX is Corvus, in his fallen angel state. He is the one who resurrected the Gittish Empire and the dark dragon Barbarus so he could destroy the mortals of the Protectorate, in retribution for the betrayal and suffering he endured.
The Final Boss in X is Nelgel the Netherfiend. When confronted by the Hero, he attempts to defeat him/her using his humanoid form, and later his beastly form. Upon being defeated, he warns of dark powers beyond his control before dying, and although the Hero was successful in escaping, he/she wasn't able to break the seal of darkness over Rendashia.
The Final Boss in XI is Calasmos. A malevolent being of impressive power hailing from beyond the stars, also known as the Dark One, he is responsible for the sorcerer Morcant betraying Erdwin, allowing for his transformation in Mordegon. While reduced to a corrupted Spirit of Lost Time in the original timeline and unable to acquire his original body, which was sealed in Erdwin's Lantern, he was able to follow the Luminary into the altered timeline, using the second demise of Mordegon to achieve unity once more. Upon his destruction, Calasmos rues his defeat but not before telling the party that light cannot exist without darkness and another will someday take his place.
